260 A. E. Verrlll—Molhisca of the Neio England Coast. 



side, is regularly elliptical and pretty clearly defined by the ridges 

 rimning from the beak to the posterior tip ; this area is covered by 

 rather prominent, thin, or somewhat lamelliform, divergent ribs, 

 which are regularly and rather closely arranged and somewhat nar- 

 rower than their interspaces, distally ; these ribs usually cover the 

 whole surface, close up to the dorsal edge, which forms a somewhat 

 prominent, sharp and nearly straight carina, but is not compressed 

 and thin, as in some other related species. Within the dorsal area 

 there is no circumscribed area, such as figured by D'Orbigny in L. 

 Ja^naicensis, with which Mr. Dall identifies our shell. Moreover, the 

 anterior lunule, rei^resented as very distinct in the latter, is obscure 

 and often entirely wanting in our shell. When visible at all, the 

 lunular area is narrow, elongated and defined only by the interrup- 

 tion of the concentric ribs, just before reaching the hinge-margin, 

 leaving a nearly smooth dorsal area between the umbos. Moreover, 

 on the anterior end of the shell there are two rather faint, slightly 

 raised ridges, or waves, a short distance apart, extending from the 

 beak to the anterior ventral margin, and having the area between 

 them slightly concave, corresponding to a flattened or slightly con- 

 cave space on the margin, where it terminates ; this slight undula- 

 tion, bordered by two small crests, is, however, usually less distinct 

 than represented in our figure. The posterior end is decidedly acute 

 with a distinct emargination below it, but the ridge, which runs 

 from the beak to the posterior tip, though somewhat prominent, is 

 obtusely rounded and decidedly less developed than in L. Jamai- 

 censis. The concentric ribs are clearly defined, usually very regular, 

 obtusely rounded, or frequently with the edge reflexed anteriorly, 

 and often rising into little angles or points in crossing the posterior 

 ridge ; the interspaces are rather deep, nearly smooth, and usually 

 about twice the breadth of the ribs on the sides of the shell. The 

 epidermis is closely adherent and usually dark olive-green. 



Well-grown specimens are frequently 13""" long; 8""" broad; and 

 6"'"' thick ; from the beak to the posterior tip, 8""". 



A species closely related to this, but evidently distinct, which is 

 most likely the true L. unca Gould, was dredged by the Albatross 

 off Cape Hatteras in 14 to 48 fathoms, in considerable numbers. 



This shell is more solid, more ovate, and more swollen medially, 

 with the beak nearly central, the posterior end very acute, and the 

 posterior dorsal margin slightly concave, while the concave dorsal 

 area is defined by a rounded and not very prominent ridge. The 

 umbos are nearly smooth, polished and lustrous in the adult dead 



