416 



CRETACEOUS LAMELLIBRANCHIA. 



extending- from the umbo postero-ventrally, but this often becomes indistinct in 

 the later stages of growth ; the posterior part of the valve (behind the carina) is 

 convex, except the postero-dorsal part near the umbo, which is concave, and here 

 the margin is more or less concave. The surface of the valve is smooth, except 



246 



247 



248 



Figs. 243 — 248. — Exoyyva colamba (Lam.). Zone of Pecten asper. 243 — 245, Evershot. 246 — 248, 

 Eggardon Hill. 243 — 247, left valves. 244, posterior view of 243. 248, right valve and left 

 umbo of 247. Sedgwick Museum, Cambridge. All x |. 



for growth-lines. Right valve flat, or slightly convex or concave, sometimes 

 undulating. Umbo small, spiral. 



Affinities. — This species is allied to E. conica, but the carina is less distinct 

 and more rounded, the posterior part of the left valve is less flattened, and the 

 spire of the left umbo is better developed. 



Remarks. — Since the name given by Lamarck in 1819 (columba) has been used 

 by the majority of later writers it seems better to retain that, rather than attempt 

 to revive the little-known name given by the same author in 1802. 



