41 



Pentamerus galeatus. (Dalman.) 

 This species occurs between Cape Gasp^ and Cape Rosier in No. 1. 



Eenssel^ria ovoides. (Eaton.) 



Plate 3, figs. 7, Tor, lb, 10, 10a. 

 RENSSELiERiA OVOIDES, Hall ; Pal., N.Y., vol. 3. 



Description. — The usual form of the larger specimens of this species is- 

 elongate ovate ; sides nearly straight or gently convex as shown in figs. 

 7, la. The smaller individuals (figs. 10, 10a.) are alway wider in 

 proportion to the length and more pointed in front than the larger. In 

 the proportions, there is a gradual passage from specimens in which the 

 width is equal to the length, or even a little greater, to those which the 

 length is twice the width. The ventral valve is the most convex 

 of the two, usually obscurely rounded, angular along the middle, 

 with a gently convex slope towards the sides ; a portion of the margin 

 bent at nearly a right angle towards the opposite valve. The outline on 

 a side view is most elevated about the mid-length or a little above ; 

 abruptly curved down over the umbo to the beak, more gently and 

 uniformly arched to the front margin. Umbo moderate, rising one 

 or two lines above that of the opposite valve ; beak closely incurved 

 down to and in contact with the dorsal umbo. The depth of this 

 valve is sometimes nearly equal to its width. Dorsal valve moderately 

 convex, most elevated along the median line where it is rounded angular, 

 with a gently convex, flat, or even slightly concave, slope towards the 

 sides; a portion of the margin bent at nearly aright angle, as in the 

 ventral valve. The umbo is only slightly prominent, the beak always con- 

 cealed beneath the opposite beak." 



In the young individuals, the angulation along the median line of both 

 valves usually extends to the front margin ; but, as the shell becomes 

 larger, the anterior half or two-thirds becomes uniformly depressed, con- 

 vex, and the angulation disappears. 



Surface with fine radiating stride, five to ten in the width of two lines. 

 These striae are most distinct at the front margin, and become obscure or 

 die out altoo-ether above the mid-leni2;th of the shell. Some- 

 times the upper one-third of the shell is quite smooth. The 

 shell is also marked by a variable number of concentric wrinkles of 

 growth, which give the outlines of the shell at all ages, and show how the 

 same individual gradually changed from the broad to the narrow form as 

 it increased in size. In general the specimens from the limestone are 

 smoother than those from the sandstone. 



