420 EEPORT OF COMMISSIONER OF FISH AND FISHERIES. 



Leptochelia Dana. 



Leptoclielia Dana, Am. Jour. Sci., II, vol. viii, p. 425, 1849; U. S. Expl. Exped., 



Crust., p. 800, 1853. 

 Paraianais Dana, Am. Jour. Sci., II, vol. xiv, p. 306, 1852; U. S. Expl. Exped., 



Crust., p. 798, 1853. 



Antennulse and antennae simple ; mandibles without palpi ; pleon 

 composed of six segments, bearing five pairs of ciliated pleopods below, 

 and a pair of biramoiis nropods behind ; incubatory pouch of the females 

 of the normal form. 



The genus Leptochelia was constituted by Professor Dana for a form 

 which Fritz Miiller has since shown to be the male of Paratanais Dana, 

 and although so far as I know the name has not hitherto been used 

 for any but the male forms, I see no reason why it should not be 

 adopted instead of the later name Paratanais. I have therefore adopted 

 it for the four species lately described, from our coast. Dr. Stirapson's 

 Tanaisfilum undoubtedly belongs to the same genus, making five species 

 within our limits, only four of which I have seen. The species that I 

 have examined may be further characterized as follows : The body is of 

 nearly uniform size throughout. The anteunulae are directed forward 

 and have a large basal segment, in contact with its fellow of the opposite 

 side at its origin, and composing about half the length of the organ in 

 the females ; but in the males this segment, though absolutely much 

 larger than in the females, may not form more than about a third of the 

 total length of the antennula, which is nine to twelve jointed and termi- 

 nated by a well developed flagellum. The autennse differ but little in the 

 sexes, and are five-jointed. The organs of the mouth are abortive in the 

 males, and the oral region is covered below by a pair of subtriangular 

 plates, perhaps the rudiments of the maxillipeds. The second thoracic 

 segment is shorter than those that follow it ; the fifth and sixth are the 

 longest, and the seventh is shorter than the sixth. 



The pleon consists of six distinct segments, subequal in length or 

 with the last somewhat longer than the others. These segments are 

 smooth above, and the first five bear on their under surface each a pair 

 of pleopods, much like those of Tanais (pi. XIII, fig. 82), but not cili- 

 ated on the basal segment. The last segment bears a pair of uropods, 

 which consist of a large basal segment bearing two terete rami. Of 

 these the outer ramus is shorter and smaller than the inner, and may 

 consist of a single segment so small and short as to be easily overlooked ; 

 the inner ramus is larger and longer, and composed, in our species, of 

 from two to six segments. The number of these segments appears to 

 be of value as a specific character, but not perfectly constant. 



In the females the incubatory pouch is formed, as in the order gener- 

 ally, by four pairs, of lamellae attached to the bases of the second, third, 

 fourth, and fifth pairs of legs. 



