141 



They are separated from each other by a narrow fissure which extends 

 quite to the beak. Beneath, they are supported by two very slightly 

 developed vertical and parallel plates. From their anterior extremities 

 two slender calcified oral processes extend about one-fifth the length of 

 the shell, curving upwards nearly to the inner surface of the ventral valve. 

 In the cavity of the umbo there is no divaricator process, as there is in 

 Orthis. 



This species is closely allied to P. rectus (Pander) = Spirifer rectus 

 (De Verneuil) in the geology of Russia, but is not so numerously ribbed. 



The specimens are about 6 lines in length, and the same in width. 



Locality and Formation. Pauquette Rapids, on the River Ottawa. 

 Black River limestone. 



Collector. E. Billings. 



RHYNCHONELLA FRINGILLA. (N. sp.) 



a b 



Fig. 118. 

 Fig. 118. Rhynchonella fringilla. a, Side view ; b, dorsal view. 



Description. Shell large, strongly convex, transversely elliptical, 

 greatest width about the middle, length about one-eighth less than the 

 width. Ventral valve convex, with a wide concave mesial sinus, which 

 extends to the umbo, bordered on each side by two or three ribs more 

 prominent than the others, 4 or 5 strong depressed convex ribs in the 

 sinus, and from 8 to 10 on each side ; beak closely incurved down to 

 the umbo of the dorsal valve, a smooth space on each side next to the 

 hinge-line. Dorsal valve a little larger than the ventral, with an obtusely 

 rounded umbo, and the beak deeply buried beneath that of the ventral 

 valve ; a large depressed convex mesial ridge extending from the umbo to 

 the front, where it elevates the margin ; 4 or 5 ribs on the mesial elevation, 

 those on the outside sometimes subdivided at about half their length into 

 2 or 3 ; on each side of the mesial ridge there are from 8 to 10 ribs. 



