[burwash] new species OF MARINE INVERTEBRATES 83 



to a third of the total length. The anterior margin extends in a broad 

 curve from the beak to a point on the ventral margin somewhat posterior 

 to the beak and thence a reversed curve carries the margin out to the 

 narrow elongated posteal end of the shell. On the dorsal side the margin 

 from the beak to the posteal end is a convave curve, which is interrupted 

 in the casts by a notch which represents the thickening of the shell 

 on the internal surface just in front of the adductor muscle. The 

 dorsal and ventral margins are united posteally by a convex curve. 

 The shell gaped slightly at this end, and the aperture was constricted 

 in the middle by a sharp ridge, which projected from the interior of 

 the shell and is represented by a groove in the cast. This groove extends 

 forward from the posteal margin with an upward curve to a point in 

 the dorsal side about half way from the posteal end to the notch. 



There is no lunule, but a well developed escutcheon extends nearly 

 to the posterior end of the shell. The surface of the shell adjacent to 

 the cardinal margin has a non-costated area which extends downward 

 to the ventral side near the posteal end, and is bounded below by a line 

 extending from this point on the ventral margin, with a slight downward 

 convexity to the inner posteal side of the beak. This area is marked 

 by fine growth lines. The first eight costae, counting from the posteal 

 end, are narrow, tuberculated and close together, and extend vertically 

 from the edge of the non-costated area to the ventral margin. Anterior 

 to this the next costa, after extending downward from the dorsal 

 margin at the adductor scar nearly to the ventral margin curves rather 

 sharply forward and upward, then downward and forward until it 

 terminates at the anterior margin. The succeeding costœ extend lesser 

 distances downward before curving forward, until those near the beak 

 have no vertical part, but cross the umbonal region in a sigmoid curve. 



The costation, which is shewn very well in the younger of the 

 two specimens, differs from that of T. scarburghensis , the most nearly 

 related species known to the writer, in being less coarsely tuberculate, 

 while the costae are more numerous, and the vertical costse of the pos- 

 terior region of this species are not present in T. scarburghensis, where 

 their place is taken by a comparatively few diagonally arranged rows 

 of tubercles. The area is also much broader in the English species as 

 figured, and is marked by rows of small tubercles which are not 

 represented in the Queen Charlotte Islands specimens. 



Trigonia recticostata (sp. nov.) 



(Plate III, Fig. 4) 



Cf. T. navis (Lam.) from clays of the inferior Oolite (lowest zone) in 

 southern Germany — see Palœontographical Society, vol. 26 (1872), 



