272 RIMULA. 



This species, large for a Rimula, approaches R. exquisita Ad. but 

 may be separated from that form by the sculpture. The concentric 

 elevated threads in passing over the ribs form nodes at their points 

 of intersection. 



American species. 

 E. FRENULATA Dall. PI. 27, fig. 54. 



Shell ovate, resembling in general shape and color a single valve 

 of Limatula ovata Wood ; apex small, laterally compressed, sharp ; 

 nucleus very minute, sculpture of fine distinct radiating threads, 

 with an intercalary finer thread between nearly every pair. Con- 

 centric sculpture of about equally strong threads, which reticulate, 

 but do not pass over or nodulate the radiations ; they are not strictly 

 concentric, being somewhat flexuous or broken at the sides, and 

 somewhat bifurcated. Anal fasciole shallow, continuous from the 

 fissure to the apex, narrow and marked with semilunar incremental 

 ridges ; fissure small, shaped like the top of an exclamation point 

 ('). Interior glossy, the fasciole marked by two faint ridges extend- 

 ing to the apex; margin of the shell crenulated by the sculpture, 

 apex reaching almost or quite as far back as the posterior margin, 

 but a little raised above it, fissure a little variable in position, but 

 mostly in the anterior third of the shell ; dorsal surface gently con- 

 vexly curved. Length 6'25, breadth 3'75 ; alt. 2'3 mill. (Dall.) 



West Florida and the Keys. 



R.frenulata DALL., Blake Gastrop., p. 406, t. 28, f. 4. 



This lovely little shell is remarkably distinct from any of the de- 

 scribed species known to me. 



E. MAZATLANICA Carpenter. PI. 63, fig. 10. 



Shell small, oblong, compressed, conical ; whitish covered with a 

 thin whitish-brown epidermis ; apex planate, narrow ; surface deli- 

 cately cancellated, cancelli quadrate ; fissure subelongate, subquad- 

 rate, within suboval, calloused ; slit occupying a portion extending 

 from i to J the entire length from apex to margin ; slit-fasciole 

 extending to. apex, crossed by growth lines; margin delicately cren- 

 ulated. 



Mazatlan, on Spondylus calcifer. 



Rimula mazatlanica CPR., Cat. Mazat. Sh. p. 222, 1857. AD., in 

 Thes. p. 210, f. 6. 





