2 28 Bulletin 29 392 



proportionally higher than Heilprin's figure of the type of perla- 

 mellosa, with more prominent beaks. The umbonal ridge is 

 slightly curving resembling that of ►S". Leana ; the entire surface 

 is ornamented with very regular sharp, concentric lamellae, on 

 the center of the disc there are about eight to every ten mille- 

 meters while in perlamellosa there are about ten ; radial striae 

 very faint, much closer than in perlamellosa. Length 66, altitude 

 55, semidiameter 9 mm. The interior of the valve is concealed 

 by a hard matrix. 



This very beautiful shell is the first of the genus ever found 

 in the Santo Domingo blue clays though Gabb reported kS. varie- 

 gata Lamarck from the Post Pliocene Coast limestone at Macoris. 

 Our shell is named in honor of Mr. H. H. Clayton of the Meteoro- 

 logical Bureau, Buenos Aires, as a token of highest regard and 

 friendship. 



Localities. — (Kxp'd '16) Zone I, Rio Cana at Caimito ; 

 Bluff 2, Cercado de Mao. 



Genus Psammosolen Risso 

 Psammosolen Sancti-Domi?iici, n. sp. 

 Plate 37, Figure 13 



Shell thin, delicate, with a broad shallow sulcus passing from 

 the umbo to the ventral margin ; dorsal and ventral margins sub- 

 rectilinear, almost parallel ; surface marked by occasional, concen- 

 tric growth lines, and very elegantly chiseled with close-set, 

 slightly wavy, parallel, incised lines which run in an oblique direc- 

 tion over the posterior and central part of the valve, but at the 

 anterior end their distal ends turn forwards and upwards in 

 graceful curves ; very near the anterior dorsal margin the incised 

 lines are obsolete. Although all our specimens show very nearly 

 the same sculpturing, this may not be a very constant character. 

 Pallial sinus tongue- shaped, very deep, extending forward into 

 the anterior third of the valve. Length of shell 27, altitude 12, 

 semidiameter 4 mm. 



P. vicksburgensis Aldrich is listed by Dall from Bowden, but 

 our shell has an elegance and precision of form and sculpture 



