67 



convex or parallel for two-thirds the length, then converging to the apex, 

 where they meet at an angle of between seventy and eighty degrees. In 

 one of the two specimens collected there is a flat margin on each side one- 

 sixth the whole width of the shell. Between these two flat margins the 

 remainder of the shell is gently convex. In the other specimen this cen- 

 tral space is slightly convex in the anterior part of the shell, but on 

 approaching the beak it becomes an angular roofshaped ridge. The 

 shell is thin, black and shining with obscure fluctuating, concentric undu- 

 lations of growth, and with very fine, obscurely indicated, longitudinal 

 striae. 



Length, nine lines ; width, five lines. 



LiNGULELLA? AFFINIS. (N. sp.) 

 Fig. 35. 



Description. — Ventral valve elongate, conical or acutely triangular 

 Apical angle about 45°. Front margin gently convex in the middle, 

 rounded at the angles ; sides nearly straight, uniformly converging from 

 the anterior angles to the beak. Surface with very fine longitudinal striae 

 about ten in the width of one line. 



This species is founded upon Ihe single specimen of a ventral valve 

 above figured. The upper two-thirds is partly worn away in the middle 

 leaving only the outline in the stone. It appears to have been; when per- 

 fect, gently convex, the rostral portion near the beak semi-cylindrical. 

 Length, about thirteen lines ; width, nine lines. 



The dorsal valve has not been identified. 



LiNGULELLA? SPISSA. (N. Sp.) 

 Fig. 36, a, b, c. 



Description. — Shell sub-pentagonal, or sub-ovate ; length and width 

 about equal, sometimes strongly ventricose. Dorsal jvalve with the front 

 margin straight or very gently convex for about two-thirds the width in 

 the middle ; anterior angles rounded ; sides straight or slightly convex 

 and sub-parallel until within one-third or one-fourth the length from the 

 beak, then converging to the apex, where they form an obtuse angle 

 which varies from 100 to about 110 degrees. This valve is generally very 

 convex, sometimes almost hemispherical, the outline on a side view is 

 rather abruptly elevated in the rostral third, depressed convex for a short 

 space in the middle, and then more gently descending to the front mar- 

 gin. Most of the specimens of this valve arc eight or nine lines in length, 

 and about the same in width. 



