18 



In some specimens, the cardinal edge of the ventral valve is quite sharp, 

 and does not exhibit any indications of spines. In others there are four 

 or five small tubercles or rudimentary spines, on the cardinal edge. 

 When they can be seen they appear to be short, nearly erect or curving 

 , lightly inwards, as represented in the figure above. The following are 

 the dimensions of several specimens in lines, the first number in each 

 case being the width, 6-3^ ; 16-10 ; 20-12 ; 22-12 ; 24-14. 



Small specimens of this species have nearly the proportion of C.melonica 

 but are always nearly flat, while those of the latter are always more 

 convex. 



Locality/ and Formation. — This species occurs at Perce, Bay of Chaleurs. 

 Lower Devonian. 



Collector. — Sir W. E. Logan. 



Chonetes Dawsoni. (N. sp.) 



Fig. 8. 



Fig. 8.— Chonetes Dawsoni. Ventral valve. 



Description. — Shell semi-elliptical ; width about one-third or one-fourth 

 greater than the length ; cardinal angles usually somewhat less than a 

 right angle : sides, for about one-third or one-half the length below the 

 hinge line, nearly straight, or gently convex ; slightly converging towards 

 each other, and then gradually and uniformly curving to the front margin 

 which is broadly rounded. 



Ventral valve gently concave, or nearly flat ; the umbo slightly ele- 

 vated ; beak scarcely distinguishable from the cardinal edge. On the 

 latter are from six to ten short spines on each side of the beak, sloping 

 outwards at an angle of from 45° to 60°. The cast of the interior of this 

 valve shows that there is a thin elevated ridge or septum, extending from 

 the beak along the median Hne, about half the length of the shell. Two 

 other obscure ridges diverge from the beak outwards, forming an angle of 

 between 30^ and 40° with the hinge line. The area has not been seen, 

 but its impression shows that it is of moderate size, and inclined at an 

 angle of about 45° to the plane of the lateral margin. Foramen triangu- 

 lar, the width apparently a little greater than the height. 



