190 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 93 



densely and coarsely granulate, the granules apparently arranged m 

 radial lines. Internally the right valve has a strong cardinal tooth 

 that fits into a socket in the hinge of the left valve, and there is a 

 rather stout internal ligament posterior to the tooth. The ventral 

 margin is radially furrowed in the right valve, smooth in the left; 

 the pallial line is simple. 



The type, U.S.N.M. No. 536152, measures: Length. 7.3 mm.; height, 

 6.4 mm.; breadth, 5 mm. It was dredged in TO fathoms off Del ray 

 Beach, Palm Beach County, Fla. 



This differs from Poromya gra/rwlata Nyst and the other West 

 Atlantic Poromyas in its rostrate form and larger, more crowded 

 granules. It occurs from Cape Hatteras, N. C, to Barbados. 



Genus CAECUM Fleming, 1813 



CAECUM (CAECUM) CAYOSENSE, new species 

 Plate 20, Figure 9 



Shell white, stout, arcuate, ornamented with 14 strong annular 

 ribs of somewhat varying size. The interspaces are of the same 

 widths as the ribs, or wider, and are ornamented with fine axial 

 riblets, which tend to become obscure on the annular ribs. At 

 intervals opaque white axial lines stand out against the ground color 

 of a more glassy white. The septum bears a rather long pointed 

 protuberance at the edge nearest to the convex side of the shell. 



The type. U.S.N.M. No. 536045, was collected by Dr. B. R. Bales 

 at Bonefish Key, Florida Keys. It measures : Length, 3.2 mm. ; width 

 (at lowest rib), 1.3 mm. 



This Caecum differs from all the other West Atlantic species in 

 possessing fewer and stronger, more distantly separated ribs. 



Genus FARTULUM Carpenter, 1857 

 FARTULUM NEBULOSUM. new species 



Plate 20, Figure 8 



Shell small, arcuate, smooth, except for fine growth lines, vinaceous- 

 brown, with irregular, white annular splotches of varying widths, 

 often more or less wavy. x\pex constricted, closed with an acuminate 

 septum, the point near and directed toward the concave side of the 

 shell. The aperture is slightly constricted, lip thin, simple. Oper- 

 culum horny, circular, with many concentric whorls. 



The type", U.S.N.M. No. 536042, Mas collected by Dr. B. R. Bales 

 at Bonefish Key, Florida Keys, and measures: Length, 2 mm., width, 

 0.6 mm. 



