246 APPENDIX TO THE SUPPLEMENTS TO 



Shell sub-pentagonal, longer than wide, tapering posteriorly, broadest at its anterior 

 half, truncate or slightly rounded in front. Dorsal valve moderately convex, ventral 

 valve deeper and more convex than the dorsal one; beak produced, very slightly incurved, 

 and truncated by a small foramen margined anteriorly by an elongated deltidium in two 

 pieces. Lateral portions of the valves often much thickened. Surface of valves covered 

 with delicate radiating riblets, increasing in number at intervals by the interpolation of 

 shorter ribs. Two specimens measured respectively — 

 Length 12, breadth 9, depth 5 lines. 

 Length 11, breadth 6^ lines. 



Obs. — In his description of this fossil Mr. W. Keeping says : " This shell varies 

 considerably ; the typical shell is pentagonal in form, but some specimens have the long 

 sac-like shape of T. digona ; they vary also in the length of the shell and coarseness of 

 striation ; the latter is, however, always much more delicate than in T. Davidsoni. The 

 last-named species is the nearest ally of T. Keepingii, and is the only one with which it 

 could be confounded. Our new species is distinguished by its greater length, especially 

 length of beak and area, its steep sides, truncated front, and delicate striae. It is an 

 extremely well-marked type, although, as I have shown elsewhere, the passage forms have 

 been found connecting it with T. Davidsoni." 



I am myself strongly impressed with the idea that T. Keepingii is only a variety of T. 

 Davidsoni, but as Mr. Keeping has seen a much larger series of both species I am willing 

 provisionally to keep both forms separate. 



Middle Neocomian, Brickhill, Bedfordshire. 



6. Kingena ? rhomboidalis, W. Keeping. Dav., Appendix to the Supplements, Vol. 



V, PI. XVIII, fig. 10, 10 a, 6. 



Megerlia (Kingena) rhomboidalis, Keeping. The Fossils and palaeontological 



affinities of the Neocomian De- 

 posits of Upware and Brickhill, 

 Cambridge, p. 128, pi. vii, fig. 3, 

 1883. 



" Shell rhomboidal, slightly longer than broad, moderately convex, thickest near the 

 beaks, surface smooth, shell structure coarsely punctate. Dorsal valve obtusely trigonal, 

 convex, especially near the beak. Hinge-line gently curved; front obtusely pointed. A 

 distinct line extending three quarters the length of the shell indicates the internal dorsal 

 septum of the genus. Ventral valve rhomboidal, obscurely keeled from back to front. 

 Beak sharp, beak ridges acute, area elongated, flattened, and concave, deltidium in two 

 pieces; foramen small. Length 9^ mm., breadth 9 mm." (Keeping.) 



Obs. — I have seen only one specimen of this shell,, the type in the Woodwardian 



