77 
A VIC UL A costata. 
TAB. CCXLI V.—Fig. i. 
Syn. Avicular costata. Smith’s Strat. Syst. p . 
67 and 81, Strata Ident. Clay over 
the Upper Oolite , Jig. 8. 
Spec. Char. Deep valve gibbose, transversely 
obovate, with eight smooth costae ; ears nearly 
equal : shallow valve nearly flat, with many 
radii ; anterior ear large, produced ; posterior 
ear small. 
Although this is a thick shell the inside of the deep 
valve has farrows corresponding to the large elevated 
ribs, which also project beyond the margin. The posterior 
ear of the flat valve is divided from the rest of the shell 
by a deep narrow sinus, on the sides of which are a few 
sharp teeth , the radii upon this valve are numerous 
thread-like ridges ; the edge is entire and thick : the 
whole shell is smooth. 
A characteristic shell in the Clay upon the upper or 
great Oolite ; the specimens figured are from Bradford. 
I have others from Charter House, Hinton, near Bath. 
The same species seems to occur in the Cornbrash, 
as Smith states. I have an imperfect specimen from that 
stratum along with the Avi. echinata. 
