626 REPORT OP COMMISSIONER OF FISH AND FISHERIES. 



ernarginate in the center, but not deeply fissured. In contraction the 

 body is broader posteriorly. Dorsal surface a little convex ; lower side 

 side flat. Acetabulum round, rather small, about half the diameter 

 of the body in the contracted state, but nearly as broad when the body 

 is fully extended. The intestine shows through the integument dis- 

 tinctly ; it is slender, and makes about seven turns or folds. Color 

 pale yellow, with minute white specks beneath and on the upper sur- 

 face anteriorly, giving" it a hoary appearance ; middle of the dorsal 

 surface irregularly marked with flake- white ; laterally reticulated with 

 fine white lines. 



Length in extension, 25 mm 5 breadth, 4 mm ; in partial contraction, 

 18 mm long; 5™** to 6 mm wide. 



New Haven, parasitic in the branchial cavity of the round clam ( Venus 

 mercenaria), October, 1S71. Philadelphia, in the same clam (Leidy). 



GYMNOCOPA. 



Tomqpteris, species undetermined, (p. 453.) 



Young specimens of a species of this genus were taken in the even- 

 ing in Vineyard Sound. They are too immature for accurate identifica- 

 tion. 



A large and fine species of Tomopteris was taken by Mr. S. I. Smith, 

 in Eastport harbor, in July, 1872. This was about 40 mm in length. An 

 excellent drawing of it was made by Mr. Emerton from the living 

 specimens. It is, perhaps, the adult state of the Vineyard Sound 

 species*. 



CH,ETOGNATHA. 



Sagitta elegans Verrill, sp. no v. (p. 440.) 



Body slender, thickest in the middle, tapering slightly toward both 

 ends. Head somewhat broader than the neck, and about equal to the 

 body where thickest, slightly oblong, a little longer than broad, obtuse, 

 rounded in front or sub-truncate, sometimes with a slightly prominent 

 small central lobe or papilla ; the anterior part of the head rises into a 

 crest-like median lobe considerably higher than the posterior part; 

 ocelli two, minute, widely separated, on the posterior half of the head '■> 

 the anterior lateral borders of the head are slightly crenulated. The 

 fascicles of seta? or spinules on the sides of the head each contain about 

 eight seta?., which are considerably curved, with acute tips, and reach 

 as far as the anterior border of the head. Caudal fin ovate; its poste. 

 rior edge broadly rounded. The posterior lateral fins commence just 

 in advance of the ovaries, and extend back considerably beyond them, 

 so as to leave a naked space somewhat less than their length between 

 their posterior ends and the caudal fin ; on this naked part, just in ad- 

 vance of the caudal fin, are two small, low, lateral papilla? connected 

 with the male organs ; two other smaller papilla? are situated at about 

 the posterior third of the lateral fins. The median lateral fins are about 

 equal in length to the posterior ones, and separated from them by a 



