132 



wrinkled costellae, which pass without interruption across the 

 larger escutcheon. The upper surface of the valve is almost 

 entirely occupied by a large concave escutcheon, which is con- 

 spicuously costellated transversely throughout its length; its 

 breadth exceeds that of the area from which it is separated only 

 by a faintly elevated ridge. The rest of the valve has a series 

 of about twenty-six rows of small, closely placed, rounded, and 

 slightly crenulated costse, all of which originate at the carinal 

 angle of the valve and pass downwards nearly perpendicularly. 

 . Obs. This fossil, together with the other Cretaceous Trigonise, 

 approaches nearest in form to those of our recent species. It is 

 met with in the Chloritic Marls of Chardstock 



TRIGONIA VICARYANA, Lye., plate v., fig. 6. 



MONO. BEIT. Foss., TEIGONIJS, Lye., Pal. Soc., p. 141, plate xxv., figs. 8, 9. 



Shell ovately elongated, convex, produced and pointed at the 

 umbones, depressed posteally ; umbones sub-anterior, elevated, 

 pointed, and recurved; anterior side short, its border curved 

 elliptically, with the lower border ; area wide, flattened, its sur- 

 face, together with the escutcheon, equal to about two-fifths of 

 the entire valve, and is covered by a very delicate and numerous 

 series of obliquely curved scabrous costellae, which nearly disappear 

 in its posteal portion. The escutcheon is of moderate breadth, 

 separated from the area only by the border of the concave sur- 

 face, and by two great prominences of the costellse. The rows 

 of costse, which are very numerous and small, are curved obliquely 

 downwards. 



Obs. T. Viewryana is also met with in the Chloritic Marls of 

 Chardstock. 



TRIGONIA ALIFORMIS, Park., plate v., fig. 8. 



MONO. BEIT. Toss. TBIGONLE, Lye., Pal. Soc., p. 116, plate xxv., figs. 3-6- 



Shell sublunate, inflated anteally, produced, attenuated and 

 depressed posteally, umbones much elevated, antero-mesial, 

 pointed, much recurved and incurved, anterior side produced ; its 

 border rounded ; lower border rounded but somewhat excavated 



