/. Eights on a Crustacean from the Antarctic Seas. 



391 



Art. XXXIY. — Description of an Isopod Crustacean from the Ant- 

 arctic Seas, with Observations on the New South Shetland's ; by 

 James Eights. — With two plates. 



[It is a fact of interest in the geographical distribution of ani- 

 mals, that the largest number of species of the group of Tetra- 

 decapods (the 14-footed Crustacea), and those also of the largest 

 size, are found, not in the tropics, but in the temperate and frigid 

 zones. Among known species, the ratio for the tropics and ex- 

 tratropics, as I have shown, is 150 : 530, or over three times as 

 many occur in the extra-tropics as in the tropics. In my memoir 

 on the Geographical Distribution of Crustacea, I have stated that 

 out of the 49 recognized genera of Isopods, only 19 occur in the 

 tropics ; of 20 genera of Anisopods, only 6 occur in the tropics ; 

 and out of the 50 genera of Gammaridea, only 17 contain trop- 

 ical species. Among the Isopods, the tribe of Idotaeidea is es- 

 pecially numerous in cold-water seas ; the ratio of extra-tropical 

 to tropical species being 8:1; and two-ninths of the extra-tropical 

 belonging to the frigid zone. Moreover the frigid or subfrigid 

 zone affords the largest of known Idotseidse, one or more of them 

 three to four inches in length, while the tropical species hardly ex- 

 ceed an inch. The Glyptonotus of Eights, from the New South 

 Shetlands, is one of these giant species, the length of his specimen 

 being 3-J- inches. It therefore takes the lead among Isopods, and 

 even among all Tetradecapods, and derives thence a peculiar in- 

 terest. It was described in the 2nd volume of the Albany Insti- 

 tute, and represented by two fine plates engraved by Mr. J. 

 E. Gavit. Through the kindness of Mr. Gavit we are allowed 

 the use of the plates, and therefore here republish the description 

 of Dr. Eights. It is not clear that the genus Glyptonotus is 

 actually distinct from the older one of Idotsea. Yet it will prob- 

 ably be sustained on the ground of the form of the head, the 

 character of the abdomen, and perhaps the distinctive peculiari- 

 ties of the 6 anterior legs. Part of the characters mentioned in 

 the description are involved in the fact of its belonging to the 

 Tetradecapoda. Still we cite it entire, as published. 



The same volume of Transactions of the Albany Institute 

 (pp. 58-69,) contains Kemarks by the same author on the New 

 South Shetland Islands, from which we make citations, after 

 giving the description of the Crustacean. — j. d. d.] 



Genus GLYPTONOTUS, Eights. 



Animal composed of a head, thorax, and post-abdomen, consti- 

 tuting in all thirteen distinct segments. 



Head deeply inserted into the cephalic segment of the thorax. 

 Eyes sessile, and finely granulate. Antennce, two pairs, placed 



