84 THE ROYAL SOCIETY OF CANADA 



also Agassiz's Trigonies, Tab. 1, and Quenstedt, 'Der Jura,' Tab. xliv, 

 fig. 3. 



In this species, which is represented only by a cast of the left valve, 

 the beaks are very far forward, being less than one fourth of the length 

 from the anterior margin. The total length of the specimen is 41 mm., 

 which may be slightly less than the original length, the depth is 32 mm., 

 and the convexity of the cast of one valve about 10 mm. The general 

 shape is trigonal. The cardinal margin is concave from the beaks to 

 the posterior end, and is moreover slightly indented by the interior 

 buttress on the anterior side of the adductor scar. The anterior margin 

 forms a continuous curve from the beak to a point directly beneath it, 

 where a narrower curve joins the anterior to the ventral edge. The 

 latter is slightly convex. The posteal end is not well shown. 



The cardinal area is in a poor state of preservation and the escutch- 

 eon cannot be seen throughout its length. A lateral curved ridge, 

 extending from the beak to the posterior end, bounds the sub-cardinal 

 area. From this the costœ extend vertically to the ventral margin. 

 They are about nine in number and are continuous, with only slight 

 evidence of tuberculation. They do not diverge posteally as in T. 

 diversicostata (Whiteaves). In the region anterior to the beaks the 

 costse are arranged horizontally in the upper part, where they are 

 smaller than the vertical costse of the posteal region. In the lower 

 part they appear to slant downward and backward from the anterior 

 margin toward the vertical costse, with the first one or two of which they 

 form a rounded junction. 



Trigonia reniforme (sp. nov.) 



(Plate II, Figs, la, b) 



Cf. T. signala, Palseogr. Soc, Vol. 26, Plate II, from which this 

 species diffei's in the more rounded outline of the posterior end, and 

 in the non-costate ventral area shewn in the casts, of which there are 

 three in the material examined. 



The most perfect specimen is 65 mm. long by 44 mm, deep, 

 measured from the centre of the ventral margin to a point on the 

 hinge-line about 13 mm. behind the beaks, which are broken off. 

 The greatest thickness is 31 mm. and is situated just be- 

 low the beaks, which are close to the anteal end. As viewed 

 from above the cast is bluntly rounded in front of the thick- 

 est part and tapers backward toward the posteal end, which is 

 much more narrowly rounded. Viewed laterally the general out- 

 line of the cast is a Ijroad kidney-shape, interrupted by the beaks, 

 which project near the forward end. The dorsal margin is in gen- 



