119 



straight or oblique ; the tubercles of the rows are numerous 

 crowded, closely placed and unequal. Length, four-and-a- 

 quarter inches ; height, three-and-a-quarter inches ; diameter 

 through the united valve, one inch and three-quarters. 



Obs. This rare shell occurs in the Kimmeridge clay, at 

 Kimmeridge Bay, where I have found only one specimen, which 

 I deposited in the Jermyn Street Museum of Practical Geology. 



TRIGONTA CLAVELLATA, Sow., plate x., fig. 7. 



MONO. BEIT. Foss., TEIGONLE, Lye., Pal. Soc., p. 18, plate i., figs. 1-2, 

 Damon's Geol. of "Weymouth, Sup., plate iv., fig. 2, 

 1880. 



Shell ovately trigonal, moderated elongated, convex ; umbones 

 large, obtuse and incurved, but rarely recurved ; anterior side 

 rounded, but not much produced, its lower Jextremity curved 

 with the lower border; superior border straight, lengthened, 

 sloping obliquely downward ; escutcheon flattened, its length 

 is nearly equal to half the length of the marginal carina ; 

 area narrow, flattened, or slightly convex, transversely and 

 irregularly plicated, having three carinae of which the mesial 

 carina consists of a row of delicate small tubercles ; the two 

 bounding carinse have the tubercles much larger, but depressed, 

 and closely arranged, those on the lower carina form, lengthened 

 transverse varices; a well-marked furrow borders upon the 

 median carina ; the superior half of the area is more depressed 

 than the other portion. The sides of the valves have the rows 

 of tuberculated costse, at first oblique, but the later formed few, 

 became more horizontal. The tubercles in the rows are large, 

 closely arranged, and unequal both in size and figure. Dr. 

 Lyeett considers the forms from the Lower Calcareous Grit to 

 be the types of this species, they have sixteen or seventeen rows 

 of costse in adult specimens. 



Obs. T. clavellata occurs very abundantly in the Calcareous 

 Grit at Sandsf oot Castle, and at Eingstead Bay near Weymouth. 



