36 SUPPLEMENT TO GREAT OOLITE MOLLUSCA. 



costae, whereas H. abjectus cannot be said to have any intercostal spaces, every part of the 

 surface being occupied by unequal, crowded, nodose costse ; the two large, radiating, nodose, 

 elevated varices are alike in both species, 



Tiie specimen figured is the original example, which belonged to Mr. Bean ; it has lost 

 a portion of the surface near to the lower border, and also a portion of the apex, nor will 

 it appear remarkable that only a single specimen of a shell so thin and fragile should have 

 been disengaged from a rock so intractable as the Cornbrash of Yorkshire. 



Geological Position and Locality. The Cornbrash of Scarborough, in the collection of 

 Mr. Leckenby. 



AvicuLA CLATHRATA, Lyc. Tab. XL, figs. 1 , 1 a, 1 h. 



Testa parva suborbiculari, convexo-plana, vaJva sinistra auriculis subcequalibus magnis ; 

 superjicie costis radiantihus {circa 24) acutis, regular ibus et nodosis, lineis concentricis dis- 

 tantibus decmsatis ; valva altera subplana, IcBvigata, inornata. 



Shell small, suborbicular ; the left valve with a low convexity, with large and nearly 

 equal auricles ; the surface of the valve has about twenty-four regular, acute, and slightly 

 knotted radiating costae, which are decussated by a few distantly arranged, concentric, 

 elevated lines ; the costee radiate equally over the auricles and the middle of the shell. 

 The right valve is more flattened, it is smooth and destitute of ornamentation. Diameter, 

 about three lines. 



Geological Position and Locality. The Great Oolite of Minchinhampton ; a single 

 specimen. 



AvicuLA suBcosTATA, Roemer, sp. Tab. XL, fig. 24. 



MoNOTis SUBCOSTATA, Boemev. Nord. Ool., p. 75, t. 4, p. 7. 



Testa orbiculari subobliqua, convexa, longitudinaliter costulata, subtillissime concentrice 

 striata, costuUs (10 — 14) remotis super ne evanescentibus, incequalibus, auricula lavi, 

 umhonihus minimis antrorsum incurvis. Valva sinistra. (Roemer.) 



Shell orbicular, rather oblique, convex, longitudinally costulated, and with very 

 delicate concentric striations; costellse (10 — 14) acute, distinct, rather unequal, and dis- 

 appearing towards the umbo ; auricles plain ; umbo small, curved forwards. The right 

 valve is not known. 



A small shell ; much less convex, less oblique, with a shorter hinge-line and more 

 delicate ribs than A. costata. Sow. 



Geological Position and Locality. The Great Oolite of Minchinhampton Common, at 

 which place it is very rare. 



