125 



lengthened, flattened and depressed; the area has some con- 

 vexity, more especially in the right valve ; it is bounded by two 

 deeply dentated carinse, the inter-carinal costellse are few, large, 

 and somewhat irregular ; the costse in fully developed specimens 

 are about twenty-seven, curved obliquely or subconcentric. 



Obs. T. sculpta occurs in the Cephalopoda beds and Sands 

 below of the Inferior Oolite at Bradford Abbas ; where it is a 

 rare fossil. It has been met with in the Cornbrash of this 

 county. 



TRIGONTA BELLA, Lye., plate i,, fig. 5. 



MONO. BEIT. Foss. TEIGONLS:, Lye., Pal. Soc., p. 162, plate xxxii., figs. 6-8a. 



Shell convex mesially, much produced and pointed at its 

 umbonal extremity, which is only slightly, or sometimes not at 

 all recurved ; escutcheon narrow, depressed and excavated, so 

 that no portion of it is seen when a valve is laid horizontally 

 upon its borders, and viewed from above; its length exceeds 

 twice its breadth in the united valves; the surface of the 

 escutcheon has a numerous series of very delicate, diverging, 

 slightly indented costellse ; the area is divided into two nearly 

 equal spaces by an unusually large, elevated; and nodose median 

 carina ; its costellse, eight or nine in number, are very irregularly 

 knotted or indented ; the right valve has only three or four 

 larger costellse, and its surface is more elevated, the other por- 

 tion of the shell has the costse twenty-eight or twenty-nine in 

 number, moderately elevated, very oblique, and with little 

 curvature. 



Obs. This well-characterized species of the Costatw section 

 has been hitherto only found, in the Cephalopoda bed of Brad- 

 ford Abbas, where it is rarely met with. 



TRIGONIA TENUICOSTA, Lye., plate i., fig. 2. 



MONO. BEIT. Foss. TEIGONLZE, Lye., Pal. Soc,, p. 160, plate 33, figs. 7-9a. 



Shell ovately trigonal, very convex ; umbones elevated, acute, 

 arched inwards, and recurved ; anterior side very short, its 



