128 AMERICAN MARINE CONCHOLOGY. 



Genus DIPLOTHYRA, Tryon. 

 Proc. Philad. Acad. 1862. 



1. D. SMITHII, Tryon. Fig. 269. 

 Proc. Philad. Acad. 1862. 



Shell short, ovate, divided in the middle by an oblique im- 

 pressed line, posterior to which the surface is covered with growth 

 lines only, but anteriorly it is finely and sharply transversely 

 sculptured, and obsoletely, radiately ribbed in some specimens ; 

 the umbonal plates are generally much distorted, so that no par- 

 ticular form can be traced throughout all the specimens, though 

 the more perfect approach to that depicted in the magnified 

 figure. 



Transverse axis 15, vertical 10 mill. 



(Burrowing in oyster shells.) Tottenville, Staten Island, N. Y. 



Family GASTROCELENID.^, Gray. 

 Zool. Proc. London. 1858. 



Genus ROCELLAKIA, Fleuriau de Bellevue. 



(Rupettaria.) Journ. de Physique., liv. 1802. 

 Gastrochcena (partim) Auct. 



Shell regular, equivalve; valve* ovate or cuneiform, widely 

 gaping anteriorly, very unequilateral ; umbones anterior, ligament 

 long and narrow ; pallial line lightly impressed, sinuated, uniting 

 the muscular impressions ; tube claviform or irregular, often in- 

 complete, perforating shells and limestone, to which its walls are 

 sometimes adherent. 



1. R. OVATA, Sowerby. Fig. 2 "70. 



(Gattrochama.) Zool. Proc. 21. 1834. 



Shell ovate, whitish,, longitudinally striate, strige narrow ; an- 

 terior length one-fifth that of the posterior side. 

 Length 30, alt. 17.50 mill. 



Charleston, 8. C. (W. Stimpson.) 



This species inhabits the West Indies, and also occurs on the 

 Pacific side of Central America. 



2. R. STIMPSONII, Tryon. Fig. 271. 



Proc. Philad. Acad. 1862. 



Shell narrowly elongate, white, anterior extremity very short, 

 acuminate j valves densely concentrically striate; umbones scarcely 



