80 MB. E. J. MIEES ON THE IDOTEID^. 



§§ Postabdomen consisting of more than one segment, distinct, 

 and visible in a dorsal view. (Cleantis.) 



The species may be distinguislied as follows : — 

 Postabdomen 2-jointed, its distal end subtriangulate. 



1. C. isopus, Grube (ined.). 

 Postabdomen 3-jointed, its distal end subtruncated or slightly 

 excavated. 2. C. linearis, Dana. 



Postabdomen 5-jointed, its distal end deeply emarginate. 



3. C. granulosa, Heller. 



Cleantis isopus. (Plate III. figs. 9-11.) 



Cleantis isopus, Grube (MS. in Coll. Brit. Mus.). 



The body has straight and snbparallel sides, and is rather 

 convex in the middle line ; the head has a small transverse linear 

 impression near its posterior margin ; its anterior margin is some- 

 what excavated, and its antero-lateral angles nearly right angles. 

 The anterior margin of the first segment of the body is concave ; 

 its antero-lateral angles are rounded and produced along the sides 

 of the head almost as far as the eyes, which are situated in the 

 middle of the lateral margins. The following segments of the 

 body are all of nearly similar form and equal length, and are 

 produced neither at the antero-lateral nor at the postero-lateral 

 angles. The postabdomen is composed of two distinct segments, 

 the first being very short; the terminal segment is scarcely longer 

 than broad, convex above at base, with the sides at first nearly 

 parallel, but near to the distal extremity suddenly convergent, so 

 that the apex is very broadly and obtusely triangulate ; it is 

 marked on each side near the base with sutures indicative of two 

 coalescent segments. The antennules are nearly as in Idotea ; 

 the antennae rather more than half as long as the animal, with 

 five joints visible in a dorsal view, the first two of which are 

 short, the two next longer and subequal, and the last (which takes 

 the place of the flagellum in Idotea) yet rather longer, and clothed 

 with a few scattered short hairs. The epimera are almost linear, 

 and in the first three segments extend along only half the length 

 of the lateral margins ; in the following segments they become 

 successively longer. The legs are very slender ; the fourth pair 

 are, however, but little shorter than the preceding ; the claws of 

 all the legs are slender and slightly curved. The terminal oper- 

 cular plates are three-sided, with the outer margins oblique and 



