MARINE ISOPODA OF NEW ENGLAND, ETC. 345 



lamella at the apex and very obliquely truncated. It is minutely serru- 

 late toward the tip on the side opposite the lamella. 



The males of this species sometimes attain a length of 30 mm to 38 mm , 

 with a breadth of 8 mm to 9 mm but the females are smaller, rarely, if ever, 

 exceeding 20 mm in length, with a breadth of 6.5 mm , and are found witu 

 eggs when not over 7.5 mm in length. The color varies greatly. Fre- 

 quently it is of a nearly uniform light or dark green, or brownish with 

 minute blackish punctations. It is often longitudinally striped with 

 light color, or nearly white on a dark background, and the stripes may 

 be marginal only, or accompanied, especially in the males, by a median 

 dorsal stripe. More rarely the colors are arranged transversely in bands 

 or blotches, and specimens thus marked are easily mistaken for the 

 next species. The females are usually darker than the males, and often 

 with a light lateral stripe, which may be very narrow or broken into a 

 series of blotches. 



A comparison of specimens from both sides of the Atlantic does not 

 tSeem to furnish any characters by which to separate this species 

 from the common European form, I. trieuspidata Desrn., and as 

 Say's trivial name has priority I have adopted it. I. tridentata Eathke 

 appears to be the same species, but I. tridentata, Latreille* is de- 

 scribed by that author as having antennae as long as the body ; fur. 

 ther, Desmarest, just before his original description of I. trieuspidata 

 says : " M. Latreille fait observer que cette idotee [I. entomon] est bien 

 differente de celle que M. Leach a decrite sous le ineine nom, * * * * 

 cette derniere qu'il nomme Idotee tricuspide," &c. It would not there- 

 fore appear that Latreille was at that time aware that this species 

 had a name, much less that he had himself named it I. tridentata. 

 Again, in his Cours d' Entomologie, where he copies figures, doubtless of 

 this species, from Savigny's Egypt, he applies to them the name Idotea 

 (pelagicat), not recognizing them as his own species. Bate and Westwood 

 quote I. tridentata Latreille as a synonym of I. trieuspidata Desni., and 

 their quotation t appears intended to refer to a work nearly twenty years 

 older than that of Desmarest. They do not, however, give their reasons 

 for deviating from the ordinary rules of priority, but, perhaps, con- 

 sidered as sufficient the authority of Edwards, who does the same thing. 

 Edwards' description of I. trieuspidata Desni. contains, moreover, an 

 evident error, the species being placed in a section of the genus which he 

 thus describes : " 2 Especes dout 1'abdomen se compose de trois articles 

 parfaitement distincts (le second e"tant compose de deux anneux soude"s 

 ensemble sur le milieu dii dos, mais separes par une scissure sur les 

 c6te"s)." I. irrorata is included in the same section, but under a sub- 

 section, thus correctly characterized : "aa Le second article de 1'abdo- 

 inen simple ; le troisieme offrant pres de sa base une fissure de chaque 



*Geii. Crust, et Ins., tome i, p. 64, 180G. 



tBrit. Sess. Crust., vol. ii, p. 380. The quotation reads, "Idotea tridentata Latreille, 

 Con. Crust, et Ins. 1, p. 64," and was doubtless intended for Gen. Crust, et Ins., 

 [tome] i, p. 64, [1806]. 



