126 



border truncated almost perpendicularly, and slightly exca- 

 vated beneath the umbones ; inferior border short, curved 

 elliptic-ally, hinge border sloping obliquely, and forming an 

 obtuse angle with the syphonal border, which is nearly perpen- 

 dicular, and equal in length to the hinge-border ; area large, 

 concave, its surface forming nearly a right angle with the 

 costated portion of the valve. It is rendered unequally bipartite 

 by a minute but distinct median carina in each valve; the 

 escutcheon is wide, heart-shaped, with the valves in contact, and 

 slightly depressed ; its superior border convex. The other por- 

 tion of the surface has the costse, about twenty-eight in number, 

 narrow and elevated, nearly horizontal, curving upwards anteally. 

 The hinge-processes are large and project considerably. 



Obs. This species has been met with in the Cephalopoda Bed 

 at Walditch, near Bridport, and at Bradford Abbas, but in 

 neither locality is it common. 



TRIGONIA MONILIFERA, Agass., plate ii., fig. 1. 



MONO. BEIT. Foss. TRIQONLE, Lye., Pal. Soc., p. 165, plate xxxi., figs. 

 1 2a, 10. 



T. MAEGINATA, Dam., Damon's Geol. of Weymouth, Sup. pi. iv., fig. 1, 

 1880. 



Shell ovately trigonal, very convex, both mesially and anteally, 

 umbones prominent, much incurved, and more or less recurved ; 

 anterior side moderately produced and rounded, its border 

 curved elliptically with the lower border, its superior or umbonal 

 portion slightly excavated, hinge- border concave ; escutcheon 

 very wide and concave, the surface for the most part delicately 

 reticulated, having two series of numerous small fine ridges ; the 

 area is of moderate size, bipartite, somewhat concave and nearly 

 alike in both the valves, it has a prominent median carina, and 

 the boundary carinse are large. The rest of the shell has about 

 twenty-five costae (in adult forms) which are large and somewhat 

 flattened, the lines of growth are conspicuous and prominent. 



. This species cccurs in the lower beds of the Kimmeridge 



