538 Verrill and Bush — Marine Mollusca of the Bermudas. 

 Section III. — Costulata. — Shell ribbed longitudinally. 



Caecum obesum, sp. nov. 



Plate LXV. Fig. U. 



Shell thick, relatively shoi't, stout, moderately curved, with about 

 twelve strong, obtuse, longitudinal ribs, with wider, concave inter- 

 stices ; close to the anterior end these are decussated by several 

 incised, revolving lines and close to the margin are replaced by two 

 to six cingula, one of which is sometimes more elevated than the 

 rest. Aperture round, unusually oblique, with a somewhat thickened 

 margin. Plug with a small, prominent, oblique mucro, close to the 

 outer margin. Color white, tinged with rusty brown. 



Length, 2.5"'" ; diameter, 0.75"^'". 



Csecum delicatulum, sp. nov. 



Plate LXV. Fig. 4. 



Shell small, thin, delicate, strongly curved, but little tapered, 

 covered with numerous, fine, raised, longitudinal riblets, about as 

 wide as their interstices. Near the margin, crossed by a number of 

 fine, transverse lines, which form definite cingula close to the mar- 

 gin. Aperture neai-ly round, very oblique. Plug broadly exposed, 

 oblique, most prominent near the outer margin, without a definite 

 mucro. Color white. 



Length, 2'"'" ; diameter, 0,5°^™. 



Two young specimens, referred to this species, are strongly curved, 

 regularly and rapidly narrowed posteriorly, with the surface, toward 

 the larger end, minutely costulate, but smooth and translucent pos- 

 teriorly. Plug just within the aperture, with a delicate spine close 

 to the outer margin, visible only in profile. 



In shell-sand, rare. 



Caecum debile, sp. nov. 



Shell differing from (7. delicatulum in having a prominent, nearly 

 hemispherical plug and the surface covered by less numerous, very 

 delicate, raised, longitudinal riblets, well separated but unequally 

 spaced, crossed, near the margin, by very delicate well separated 

 cingula, one of which, just below the edge, is more prominent than 

 the others. Entire surface crossed by microscopic growth lines. 



Li shell-sand, rare. 



