MONTACUTA. 205 



position not being homogeneous, the base becomes 

 hardened to such an extent, that a cup-shaped process 

 or " ossicle" is formed, which can be separated from 

 the shell. It can only be detected in fresh specimens 

 before the cartilage has dried up; and the latter is 

 seldom preserved, owing to its elastic nature and slight 

 attachment to the pit, which is fixed and forms part of 

 the shell. The genus Thracia has nearly the same kind 

 of process. 



Gould was of opinion that the present genus and 

 Kellia ought to be united, or else that the one might 

 merge in Ungulina of Daudin, and the other in Erycina 

 of Lamarck. Nyst referred Mont acuta to the last- 

 mentioned genus. But although Lamarck states that 

 the ligament in Erycina is internal, the hinge is de- 

 scribed as having cardinal as well as lateral teeth. The 

 structure of the hinge in Ungulina is very different from 

 that in Kellia. 



Several species are noticed by Dr. Philip Carpenter 

 as inhabiting the Gulf of California. 



1. MONTACUTA SUBSTRIA TA *, Montagu. 



Ligula substriata, Mont. Test. Brit. Suppl. p. 25. M. substriata, F. & H. 

 ii. p. 77, pi. xviii. f. 8, 8 a, and (animal) pi. O. f. 2. 



Body whitish and nearly transparent: mantle having its 

 margin simple, and largely open in front for the passage of the 

 foot : gills large and conspicuous : foot muscular, transparent, 

 very much longer than the shell, issuing from the broader end, 

 tapering to a disk-like point, and furnished at the heel with a 

 byssal groove. 



Shell varying in shape from a long to a short oval, with an 

 oblique outline, rather convex, not very thin, semitransparent, 

 usually of a dull aspect, but sometimes glossy : sculpture, 

 about a dozen very slight and indistinct ribs, which radiate 

 from the beak but do not quite extend to the front margin ; 

 there are also a few white longitudinal streaks, and concentric 



* Slightly striated. 



