52 



hinge line behind the beak show a gentle curve convex towards the anterior 

 side. From the direction in which these striae reach the cardinal edge it 

 would appear that the shell, when, perfect has a distinctly angular, not 

 rounded, posterior wing. Near Jupiter River in the lower part of Div. 

 3, A. G. J. Richardson. 



Fig. 18. — Fterinea curiosa. a, view of the right valve showing the 

 area of the right ; h, anterior view. 



P. suBPLANA, Hall. — A species which is either identical with or closely 

 allied to this occurs at Point Laframboise ; Div. 1, A. G. 



P. Thisbe, n. sp. — Right valve with the hinge line long and straight, 

 equal to the whole length of the shell ; posterior margin forming nearly a 

 right angle with the hinge line and nearly straight (shghtly concave) for 

 a little more than half the width, then broadly rounded into the ventral 

 margin ; anterior extremity short, the outline obliquely rounded into the 

 ventral margin which is broadly and gently convex. The body of the 

 shell is moderately convex with the usual obliquity. The wing compressed. 

 Beak small close to he anterior end. Left valve rather strongly convex. 

 Surface with very obscure radiating ribs, three or four in two lines. 

 Length of right valve on hinge line 9 lines ; height from the mid-length of 

 hinge line to ventral margin 7 lines. Only two specimens were collected, 

 one right and one left valve, the latter very imperfect. Challoupe River; 

 Div. 4, A. G. J. Richardson. 



The left valve of this species has very nearly the same form as P. 

 undata, Hall, as figured by Winchell and Marcy in the " Memoirs of 

 the Best. Nat. Hist. Soc. Vol. 1, pi. 3, f. 2. It is however more oblique 

 anteriorly and not so nearly square. 



Genus Ischyrinia, BiHings (ante p. 16.) 



I. WiNCHELLi. B.— Junction Cliff ; Div. 1, A. G. Also in H. R. 



I. plicata, n. sp. — Cast of the interior transversely ovate, moderately 

 convex ; anterior extremity in the upper fourth straight, and forming a 

 slightly obtuse angle with the hinge line, below rounded ; ventral margin 

 broadly and uniformly convex, gradually rounded from the mid-length up 

 to the posterior extremity which is acute and has its most projecting point 

 about one-fourth the height below the hinge line ; above this point ob- 



