324 KECORDS GF THE AUSTRALIAN .MUSEUM. 



Genus CoRBULA (Brtajnih-r)^ Lamarck, 1801. 

 . (Syst. Anim. s. Vert, 1801, p. 137). 



CORBULA SUPER-CONCHA, .S/A noi\ 



Sp. (Jhar. — Sliell inequilaterally subdeltoid, tumid, witli well- 

 marked posterior production ; slightly inequivalve. Valves very 

 tumid and projecting in the umbonal regions, with large and 

 highly pronounced epiostraca'- ; articulus unknown ; cardinal 

 margins strongly triangular, but without a defined escutcheon ; 

 umbos prosogyrate. Anterior ends of less width than the pos- 

 terior, tlie margins broadly rounded ; anterior slope nearly straight 

 walled. Posterior ends moderately produced, nasute but not 

 rostrate or ti'uncate ; posterior slope pronounced, flattened, or even 

 a little concave, bounded by a curved diagonal ridge. Ventral 

 margins on the anterior sides obtusely rounded, on the posterior 

 curved obliquely upwards. .Sculpture concentric and fine, both 

 valves similar. 



Ohs. — Nothing approaching this well-marked shell has been so 

 far as I can ascertain, described from our Cretaceous rocks. It 

 is referred to Curbida purely on outward characters. 



One of the most marked features is the very pronounced um- 

 bonal and inf ra-umbonal epiostracum (as I term it) in both valves, 

 imarking growth stages. This is a pronounced feature in many 

 (Jorhida, although not in all, but here these stages are important 

 and appear to be almost a specific character. The depth to which 

 the first stage extends is ^■ariable, but not infrequently occupies 

 at least half if not more of the length of a valve. The sculpture 

 is fine and linear, and without concentric corrugations as in some 

 species. 



I have failed to find any near ally in Cretaceous rocks, although 

 were C. traskii, Gabb'\ less rostrate, it would not be unlike the 

 present shell in outline ; a similar remark also applies to C. 

 huckmani, Buckman'^, an Oolitic species. 



Figures will be given in a subsequent part. 



^'■^ I oDiploy tliis term to signify that most marked of growth stages looking 

 like a shell upon a shell. 



'3 Gabb — Eeport Geol. Survey California, i, 4, 1864, p. 149, pi. xxii., f. 121, 

 121a. 



" Lycett— Siippl. Mon. Moll. Gt. Oolite, etc., 1863, pi, xxxvii., f. 8. 



