TRANSACTIONS OF WAGNER 



754 



TERTIARY FAUNA OF FLORIDA 



Shell small, thin, polished, compressed ; left valve more convex, with 

 about twenty faint, flat, rather irregular obsolete ribs, separated by narrower, 

 shallow sulci, the whole surface with minute Camptonectes striation ; right 

 valve with concentric incremental lines and a few faint threads near the beaks 

 and anterior submargin; ears small, subequal ; ctenolium present; cardinal 

 and auricular crura developed ; interior of left valve faintly fluted, but without 

 lirae. Alt. 19, lat. 18 mm. 



In some of the specimens there are a few feeble concentric undulations 

 near the beak of the left valve. 



? Section Hyalopectcn Vcrrill. 



Hyalopccten Verrill, Trans. Conn. Acad., x., p. 71, 1897. Type P. iindalus Verrill, op. 

 cit., vi., p. 444, 1885 ; = P. fragilis Jeffreys, Ann. Mag. Nat. Hist., p. 424, 1876, -\- 

 Hyalopecten dilectus Verr. and Bush, Trans. Conn. Acad., x., p. 80, 1897. 



This section differs from the ordinary abyssal Psendamiisium in being 

 concentrically undulated, and from the thin, smooth, shallow-water forms like 

 P. gronlandicus in the absence of the Camptonectes striation. These features 

 are barely of more than specific value, as they appear to be generally inter- 

 changeable, like other surface characters in this genus. The types of Jef- 

 frey s's P. fragilis are in part in the United States National Museum. They 

 agree perfectly with his description and figures (P. Z. S., 1879, p. 561, pi. xlv., 

 fig. I [inner and outer views]). The first specimens obtained were frag- 

 mentary, as was the case with P. niidatus Verrill. I have compared the speci- 

 mens received from both authors with care, and consider them conspecific. 

 P. dilectus is complete, and, except that it is a younger and smaller shell, I 

 have been unable to detect any differences, even of a varietal nature. On the 

 other hand, the specimen to which Professor Verrill has given the name fragilis 

 Jeffreys is a perfectly distinct species with marked characters, as noted by 

 Professor Verrill (op. cit., p. 81). Jeffreys in his original description describes 

 his shell (left valve) as having " numerous fine and raised striae" which " radiate 

 from the beak and cover the whole surface." How, then, Professor Verriil 

 should come to regard a shell " distinctly undulated but not otherwise sculpt- 

 ured" as the species of Jeffreys is a mystery which I cannot solve. At all 

 events, they are perfectly distinct, and the P. fragilis Verrill, non Jeffreys, 

 may take the specific name of eucymatus. It should be observed that the 

 " raised striae," or threads, described by Jeffreys, are more abundant and more 

 constant on the left valve ; on the right valve they are often nearly obsolete, 



