course to the Indian village was unmarked by any incident worthy of note. The next day about 12, having taken a supply of musk-melons as our only food, we started for Vallecitas. The afternoon was windy, and, a rare phenomenon in this region, showery. About nine or ten miles from the village, we passed some mounds covered with cinders and pumice, and on the top of one of them found a crater-like hollow, in which grow some very large caues. Shortly afterwards the strata of fresh water deposit were seen to be vertical, and were filled with a species of Gnathodon (G. Lecontei Conrad). About 4 P. M., we skirted along the northern edge of a long curved range of hills, the base of which was composed of strata of limestone dipping outwardly, and containing also Gnathodon; around these hills and mounds were concentric lines of small stones from the mountains arranged by aqueous action.

About half past five, we encamped in the bed of Cariso creek, here entirely dry; the night was stormy, but a melon apiece, and the warmth of a large mesquite fire soon made us contented. Leaving at four the next morning, we reached Vallecitas in the afternoon, without farther adventure, worthy of being here narrated.

NOTE. By the kindness of Capt. Davidson, I learn that while he was stationed at Fort Yuma, in Dec., 1853, a violent earthquake occurred; the ground in the vicinity of the Fort opened, forming fissures, from which were thrown mud, sand and water: portions of the mountains several miles distant were seen to fall, and about forty miles S. E. of the Fort, in the direction of some springs, said to be similar to those herein described, was seen an immense column of steam. It is to be hoped that some of the officers then at the post will favor science with an account of the phenomena observed.

ART. II.-On the Geographical Distribution of Crustacea; by JAMES D. DANA.

(Continued from vol. xviii, p. 326.)

V. TETRADECAPODA.

BEFORE stating the conclusions from the tables* of the Tetradecapoda, it should be observed that this division of Crustacea has been less thoroughly explored than that of the Podophthalmia, and future investigations must vary much the proportions between the species of the different regions. The coasts of Europe and the northern seas, are within the reach of European zo

As already mentioned the Tables published in the original Report are here omitted.

ologists, and have been carefully examined; while voyagers through the tropics have usually contented themselves with collecting the larger Crustacea. In the genus Gammarus, not a tropical species had been reported, until our investigations, which brought ten or eleven to light, being one-third the whole number of those of ascertained localities reported to this genus.

Some general conclusions may, however, be safely drawn from the facts already known, although the exact ratios deduced from the tables may hereafter be much modified.

I. The Tetradecapoda are far more numerous in extra-tropical latitudes than in the tropical.

The proportion in the table is 521: 146; allowing for future discoveries, it may be set down at 2: 1, without fear of exceeding the truth.

II. The genera of extra-tropical seas are far more numerous than those of the tropical.

Out of the forty-nine genera of Isopoda, only nineteen are known to occur in the tropics, and but four of these are peculiar to the tropics.

Out of twenty genera of Anisopoda, six only are known to be tropical, and but two are exclusively so.

Among the Amphipoda, out of fifty genera of Gammaridea, only seventeen are known to contain tropical species; nine are exclusively tropical, and but ten, including these nine, have more tropical than extra-tropical species. The Caprellidea and Hyperidea embrace thirty genera, fifteen or sixteen of which include tropical species.

The variety of extra-tropical forms compared with the tropical, is hence very great.

III. From the tables, the ratio of extra-tropical and tropical species in the

Isopoda, is
Anisopoda,
Amphipoda,

4:1

6:1

3:1

Among the Isopoda, the Idotæidea are the most decidedly coldwater species, and the Cymothoidea, the least so. The ratio of species for the

Idotæidea, is
Oniscoidea,
Cymothoidea,.

8:1

7:1

2:1

Two-ninths of the extra-tropical Idotæidea (or nine species) belong to the Frigid zone, and nearly one-tenth of the extra-tropical Oniscoidea (or nine species); while less than a twenty-fifth of the Cymothoidea occur in the Frigid zone, and but one of these has not also been found in lower latitudes.

Of the Amphipoda, the Gammaridea are most strongly extratropical, the proportion being for the extra-tropical and tropical

species 3:1; while the ratio in the Caprellidea, is 3:1; and in the Hyperidea, 11: 1. Out of one hundred and seventy-eight extra-tropical species of Gammaridea, sixty-six are Frigid zone species, besides two which have been found both in the Frigid and Temperate zones.

IV. The genera which extend into the frigid region are the following. The names of those more especially frigid, according to present knowledge, are italicised; and the proportion of frigid species to the whole number of extra-tropical, is mentioned in decimals, where they are not exclusively frigid.

IDOT EIDEA.-Idotea (0-3), Glyptonotus.

ONISCOIDEA. Jæra (0.25), Jaridina, Asellus (0-20), Janira (0·5), Henopomus, Munna (0·66).

CYMOTHOIDEA.-Æga (0·4).

SEROLIDEA.-Serolis (0-2), Praniza (0·15), Anceus (0.25).

ARCTURIDEA--Arcturus (0-5).

TANAIDEA.-Tanais (05), Liriope, Crossurus, Phryxus, Dajus.

CAPRELLIDEA.-Proto (0·5), Caprella (0·24), Ægina, Cercops, Podalirius. GAMMARIDEA.-Dulichia, Siphonacetes, Unciola (0·5), Podocerus, (0·5), Laphystius, Orchestia (007), Stegocephalus, Opis (066), Uristes, Anonyx, (0·9), Leucothoe (066), Acanthonotus, (075), Iphimedia (06), Edicerus (05), Gammarus (0.33), Melita (05), Pardalisca, Ischyrocerus, Michrocheles, Pontoporeia, Ampelisca, Protomedeia, Phoxus.

HYPERIDEA-Hyperia (0·14), Metœcus, Tauria, Themisto, (3·0).

The Spheromidæ are nearly all cold-water species, though not reaching into the Frigid zone. There are forty-nine known species of Spheromide in the Temperate zone, and but four in the Torrid. Serolis is a peculiar cold-water form, belonging mainly to the subfrigid and frigid regions. Orchestia is to a large extent of the Temperate zone, while Allorchestes is more equally distributed through the torrid and temperate. Amphithoe, as restricted by us, is alike common in the torrid and temperate regions; while Iphimedia, the other section of the old group, is mainly a cold-water genus.

The Hyperidea are mostly tropical genera.

V. The species and genera of Tetradecapoda are not only most abundant in the extra-tropical regions, but besides, the individuals of species appear to be more numerous, or at least not less so. At Fuegia, the quantity of Gammaridæ collected on bait dropped in the water was exceedingly large; and in no region visited by us, did we find evidence of as great profusion. The Spheromæ were also very abundant, along the shores.

VI. Moreover, the species of extra-tropical waters are the largest of the tribe. In the Frigid zone, there are Idotæidæ three to four inches long, while the average size of the tropical species is less than three-fourths of an inch; there are Spheromæ an inch long, while those of the tropics seldom exceed a fourth of an inch; there is a Lysianassa three inches long, while

the warmer seas afford only small species half an inch in length; there is a Pterelas over an inch in length, while the Egidæ of the tropics are less than half an inch. The Gammari of the tropics are small slender species, not half the size of those of the colder seas. The species of Serolis are an inch to two inches long. Thus, through the Idotæidæ, the Egidæ, Serolidæ, Spheromidæ, Caprellidea, and Gammaridea, the largest species belong to the colder seas, and the giants among Tetradecapods, are actually found in the Frigid zone.

Among the Hyperidea there is one gigantic species, belonging to the genus Cystisoma, which is over three inches long. It is reported from the Indian Ocean, but whether tropical or not, is unascertained. Of the species of this group examined by the writer, the largest, a Tauria, was from the Frigid zone.

VII. Again, the Tetradecapoda of extra-tropical waters are the highest in rank. Among the Isopoda (which stand first), the Idotæidea appear to be of superior grade, and these, as observed, are especially developed in the colder seas, reaching their maximum size in the Frigid zone. Again, the Serolidæ, the highest of the Anisopoda, are cold-water species. The Orchestia among the Amphipoda, although reaching through both the Torrid and Temperate zones, are largest and much the most numerous in the latter.

VIII. Those species of a genus that occur in the colder waters, are often more firmly put together, and bear marks of superiority in their habits. The Amphithoe and Gammari of the tropics are lax and slender species, of small size compared with those of the colder seas.

IX. There is a tendency in the colder waters to the development of spinous species. This fact is as true of the Podophthalmia as of the Tetradecapoda. Among the former, there are the thorny Lithodes, the numerous Maioids armed with spines, the Acanthodes; while the Cancroids and Grapsoids of the tropics are usually very smooth and often polished species. There are the spinous boreal Crangons, the species of which genus in the warmer seas are without spines. Among the Tetradec ods, the boreal Iphimediæ are often spinous or crested; Acanthonotus and Dulichia are spinous genera. The same tendency is seen in the third pair of caudal stylets in some cold-water Gammari, which have the branches spinulous instead of furnished with a few minute hairs like those of the tropics.

There are also some spinous Crustacea in the tropics, as the Palinuridæ and species of Stenopus. Such facts, however, do not lead to any modification of the previous remark; for the tendency observed is still a fact as regards the several genera mentioned; moreover the spinous tropical species are few in number. SECOND SERIES, Vol. XIX, No. 55.-Jan., 1855.

2

VI. ENTOMOSTRACA.

The Entomostraca have been little studied out of the Temperate zone, if we except the results of the author's labors. The described species of most of the families are, therefore, almost exclusively from the temperate regions, and we know little of the corresponding species or groups in the warmer seas. The following table presents the number of known species of the torrid and extra-torrid zones, omitting the Lernæoids:

TABLE IV.

Torrid zone. Extra-torrid zone.

LOPHYROPODA.
Cyclopoidea,
Daphnioidea,
Cyproidea,
PHYLLOPODA.

Artemioidea,
A podoidea,
Límnadioidea,

POECILOPODA.

Ergasiloidea,
Caligoidea,

*

Were we to leave out of view the researches of the author, the number of species and the proportion for the Cyclopoidea, instead of 120 to 76, would be about 3:50, thus not only reversing the ratio, but giving to the Temperate zone almost all the species of the group. Moreover, no Daphnioids and few Caligoids have been yet reported from the Torrid zone, excepting those described in this Report. The author's time when on land in the tropics was devoted mainly to the department of Geology, and consequently the fresh-water Entomostracans were not as thoroughly collected as those of the oceans. He therefore attempts to draw no conclusions from the above ratios.

A few facts may, however, be deduced with respect to some genera, and especially those of the Cyclopoidea. The following table gives the number, as nearly as known, of the species of each genus of the Cyclopoidea, occurring in the torrid and extratorrid zones. The number common to the extra-torrid and torrid zones is mentioned in brackets.

* The whole number of Cyclopoidea described previous to May, 1842, by which time the author's observations were completed, was less than twenty-five; and of the oceanic Cyclopoids, one hundred and fifty species of which the author has described, not ten were then known. We may judge from these results of a single cruise what still remains to be done in the department of Entomostraca.