CRUSTACEA. 
32 . Idotea bicuspida. n. s. 
I. corpore elongato-ovato, caudd apice bidentatd, antennis tertiam corporis partem cequantibus. 
Long. corp. lin. 14. Color, cinereus rubro maculates. 
This species appertains to the section which Latreille has characterised by the antenna exceed- 
ing in length the head and first two segments of the body. ( Nouv . Diet. d'Hist. Nat. XVI. p. 104.) 
It is readily distinguished from the species therein comprehended, by the triangular form of the tail, 
consisting of a single segment, smooth and convex above, and notched at the apex. The body con- 
sists of seven segments, the margins of which are slightly rounded olf ; the middle of each segment is 
more elevated than the sides, giving the appearance of two lateral longitudinal lines, as in the trilo- 
bites. There is an indication of a division of the caudal segment by two lateral incisions. The head 
is transversely quadrate; the eyes are convex, and situated in the angle of the head and first segment. 
The front is slightly produced, and has a shallow incisure anteriorly. The external antenna are 
five-articulate, the last joint setaceous; the internal antenna are four-articulate, and reach to the 
third joint of the external. The feet are simple, and ciliate beneath. The instrumenta cibaria agree 
with the detailed description given by Latreille, ( loco citato , p. 99,) but the mandibles have black 
horny extremities. The portal lamina which cover the branchial and ovarian appendages, open and 
close as in the preceding species, and reach to the end of the tail. 
It is a native of the Arctic Seas. 
Plate XXVII. Fig. 6. Idotea bicuspida. 
