131 

 TRIGOXIA EXCENTRICA, Park., plate v., fig. 7. 



MONO. BEIT. Foss., TEIQONLE, Lye., Pal. Soc., p. 94, plate xx., fisf. 5, 

 plate xxi., figs. 6, 7, plate xxii., figs. 1, 5, 5a. 



Shell inequilateral, subovate, rather depressed and thin in the 

 very young condition, becoming thick, with a considerable con- 

 vexity, in an advanced stage. of growth ; umbones pointed, erect ? 

 little produced, situated about two-fifths the length of the valve 

 from the anterior border. Anterior side produced, its border 

 curved elliptically with the lower border ; hinge border nearly 

 straight, or in some examples slightly concave, sloping obliquely 

 downwards, lengthened, terminating in a posteal extremity, 

 which is rounded, but attenuated; area narrow, slightly con- 

 cave near to the umbo, where the valve forms an oblique angle, 

 separating the area from the anteal portion, The other portion 

 of the shell is covered by a series of a very numerous, slightly 

 elevated, longitudinal or horizontal costee, which are indented 

 anteally by oblique intersecting lines of growth, they cross the 

 valve near to the umbo, but disappear over the posteal third of 

 the surface. The length compared with the height is as ten to 

 seven. The hinge-teeth diverge widely, the adductor scars are 

 deeply impressed, especially the anteal adductor. 



T. excentrica occurs in the Chloritic Sands of Chardstock. 



TBIGONIA MEYEEI, Lye., plate v., fig. 5. 



MONO. BEIT. Foss., TEIGONI^, Lye., Pal. Soc., p. 125, plate xxiii., fig. 6. 



Shell ovately trigonal, very convex anteally, attenuated and 

 compressed posteally ; umbones large, elevated, pointed, and 

 much recurved ; anterior side produced, its border rounded and 

 curved with the lower border, which becomes nearly straight 

 posteally near to its attenuated extremity ; the area is narrow, 

 much curved, slightly elevated, separated from the other or 

 pallial portion of the valve, by a distinct, narrow, divisional 

 angle or ridge; the anteal portion of the area is traversed 

 transversely by a numerous series of small, closely arranged, 



