356 PROCEEDINGS OF THE ACADEMY OF [PaRT II 



CYMATIIDAE. 



Cymatium pileare (Lamarck) 



Tritonium (Lmnpusia) lineatum Gabb, Trans. Amer. Philos. Soc, xv, 1873, 

 p. 211. 



The two shells are identical with recent specimens. 



Cymatium domingense (Gabb) Plate XXIX, flg. 2. 



Tritonium (Ranularia) domingense Gabb, Trans. Amer. Philos. Soc, xv, 1873, 

 p. 212. 



This species approaches C. vespaceum. (Lam.) in many respects, 

 but the more convex whorls, the prominent varices on the whorls of 

 the spire, where there are also more numerous vertical ribs, are 

 differential characters. Moreover, the embryonic shell is more de- 

 pressed, the post-embryonic whorls enlarge more rapidly, forming 

 a far thicker spire. The anterior canal is noticeably shorter. 



Length 28.7, diam. 16 mm. 



The type and a smaller specimen are no. 3226 A. N. S. P. 



Cymatium prsefemorale Maury. 



Tritonium femorale Linn., Gabb, Trans. Amer. Philos. Soc, xv, p. 213. 



Five specimens, the largest 10 cm. long. 



Distorsio constrictus simillimus (Sowerby) 



Triton simillimus Sowb., Q. J. Geol. Soc, vi, 1849, p. 48. 



Distwtia simillimus Sby., Gabb, Trans. Amer. Philos. Soc, xv, 1873, p. 212,. 



Distortio simillimus Sby., Gabb, Joum. Acad. Nat. Sci. Phila., viii, p. 353. 



The Santo Domingan form, which was named Triton simillimus 

 by Sowerby, equals the recent D. constrictus in form and size (length 

 60 to 65 mm), but differs by having the spiral threads and striae 

 between the spiral cords more conspicuous. The length of the an- 

 terior canal varies a good deal; when short it is often more reflexed. 

 Except in the detail of sculpture mentioned, this form is identical 

 with the recent D. constrictus. 



Bowden specimens are smaller, with fewer minute spirals. The 

 form reported by Gabb from the Pliocene of Costa Rica is entirely 

 like the Santo Domingan examples. 



D. gatunensis Toula, from the Gatun formation, has fewer and 

 smaller spiral threads among the striae of the intervals, but is other- 

 wise identical with the Santo Domingo race in adult sculpture; but 

 it differs specifically by the larger embryonic shell, as stated by 

 Brown and Pilsbry^o. 



The genus Distorsio seems to have had its inception in the early 



20 Proc A. N. S. Phila. 1911, p. 356. 



