379 Dominican Fossils — Maury 215 



ior central portion of the shell is sculptured with stronger radi- 

 ating and feebler concentric threads. The latter gradually 

 strengthen anteriorly, where they form a network with the radi- 

 ating threads, every intersection being knotted. The shell is ex- 

 ceedingly thin and fragile and cannot be removed from the ma- 

 trix to examine the interior. Length 23, altitude 22, approxi- 

 mate semidiameter 7 . 5 mm. 



It is curious that the Gurabo bluffs should have yielded two 

 species of this genus, rare at such horizons ; — one akin to the 

 Vicksburgian and the other apparently the ancestor of the living 

 deep sea species. 



Locality. — (Exp'd '16) Zone B, Rio Gurabo at Los Ouema- 

 dos. 



Genus Pitaria Roemer 



Pitaria { Lamelliconcha) circinata Born 

 Plate 37, Figure I 



Venus circinata Born, Test. Mus. Vind., p. 61, pi. 4, fig. 8, 1780. 

 Cytherea juncea Guppy, Quart. Jour. Geol. Soc. London, vol. 22, 



p. 682, pi. 26, fig. 13, 1866. 

 Chione circinata Gabb, Trans. Amer. Phil. Soc, vol. 15, p. 250, 1873. 

 Cytherea juncea Guppy, Quart. Jour. Geol. Soc, vol. 32, p. 531, 1876. 

 Pitaria {Lamelliconcha) circinata Dall, Trans. Wagner Inst. Sci., vol. 



3, pt. 6, p. 1269, 1903. 



FideT)&\\, Guppy's Cumana type of juncea is identical with 

 the recent circinata ; and on comparing our specimens from the 

 blue clays of the river bluffs with those from the beach at Monte 

 Cristi no constant differences are discernible. The shell is also 

 found at Gatun and is living on both coasts of Central America 

 and in the Antilles. It is at once differentiated from our other 

 Dominican species by its single, sharp, intermediate thread between 

 every two lamellae. This alternation is more marked in our fos- 

 sil than in our recent shells. Length 34, altitude 29, semidiam- 

 eter 9 mm. 



Localities. — (Exp'd '16) Zones H and I, Rio Cana at 

 Caimito. 



