24 ME. E. J. MIEES ON THE IDOTElDiE. 



Idotea Danat, sp. n. ? 



Idotea brevicauda, yg., Dana, U.S. Eospl. Exp. xiv. {Or, ii.) p. 703, 

 pi. xlvi. fig. 5 (1853). 



In this form the body is broadest anteriorly. Head transverse, 

 subtruncate in front, and not embraced by the following segment, 

 ■with the centre slightly projecting and the sides rounded. The 

 thoracic segments increase in length from the first to the last, 

 the anterior very short, or only partly visible, the three posterior 

 sublunate in an upper view, the posterior margins being concave 

 and the angles prolonged, but obtuse or nearly so. Postabdomen 

 5-jointed, the first four joints transverse and subequal, the first 

 abruptly narrower than the following or preceding thoracic seg- 

 ment, the fifth oblong, shield-shaped, the sides curving and 

 meeting behind in an angle. Eyes rather large. Antennules 

 less than half the length of the antennae, the third joint smaller 

 than the second. Antennge only 7-jointed ; the first five joints 

 correspond to the peduncle, the first three are quite short, the 

 second has the outer apex prolonged the length of the third joint, 

 the fourth and fifth are a little oblong, but shorter than the sixth 

 and seventh, the last is acute ; a few short hairs on the joints. 

 Legs subequal, increasing from the first pair to the last; the 

 claw is nearly straight, and has a largish subcorneal base. The 

 posterior plates of the operculum are triangulate, with the distal 

 angle acute (see Dana's figure). Colour brownish grey. Length 

 1 line. 



Loe. Eio Janeiro (harbour). 



It appears to be very closely allied to the foregoing, and too 

 distinct from I. marina (with which I consider /. brevicauda to 

 be synonymous) to be regarded as the young of that species. It 

 is distinguished from /. Whymperi by the form of the terminal 

 postabdominal segment, which is no broader than the preceding 

 at its base, and by the more acute terminal plate of the oper- 

 cular valves. In the outline figure no epimeral sutures are 

 visible. 



II. Postahdomen composed of three distinct segments (visible in a 

 dorsal view) ; and with one or more sutures on the side, indi- 

 cative of partially coalescent segments. (Armida, Bisso ?) 



This section includes Idotea marina (Linn.), which may be con- 

 sidered the type of the genus in its restricted sense, 



