142 



Length 15 lines, width IT lines, depth of both valves 13 lines. 



Very numerous small specimens from 6 lines in length and upwards, 

 occur with the larger. 



This species is closely allied to R. capax (Conrad), Hudson River 

 group, being of nearly the same form and size. That species, however, 

 has only 5 or 6 ribs on each side, ornamented by concentric striae, while 

 this has 8 or 10 smooth ones. 



Locality and Formation. Gull Cape, Anticosti. In Division 4, 

 Anticosti group, Middle Silurian. 



Collector. J. Richardson. 



RHYNCHONELLA ANTICOSTIENSIS. (Billings.) 



Fig. 119. 

 Fig. IW.Rhynchonella Micostiensis. a, b, c, Different views of a specimen. 



Description. Sub-pentagonal ; apical angle about 80 ; sides nearly 

 straight or slightly convex for rather more than half the length from the 

 beak, then curving to the edge of the mesial sinus ; front nearly straight 

 for the breadth of the sinus ; side view, oblong ; front, dorsal and ventral 

 sides nearly straight ; umbo of dorsal valve abruptly curved in to the base 

 of the beak of the ventral valve, which is conical, erect, and scarcely 

 incurved. Ventral valve with a deep mesial sinus becoming obsolete at 

 two-thirds the length from the base ; dorsal valve with a strong mesial 

 elevation which, on approaching the umbo, disappears, and is succeeded 

 by a scarcely perceptible sinus, which continues to the summit. Surface 

 with 18 or 20 radiating angular ridges, crossed by close zigzag imbricating 

 striae ; 3 ribs in the ventral sinus, and 4 on the dorsal mesial elevation. 



Length 7 lines, width near the front 6 lines. 



This species resembles Atrypa subtrigonalis (Hall; Palaeontology of 

 New York, vol. 1, pi. 33, fig. 12), but has a larger and more erect beak, 

 while the side view exhibits a broadly truncated base, with the dorsal and 

 ventral outlines more nearly straight. 



Formation and Locality. Hudson River group. English Head, 

 Anticosti. 



Collector. J. Richardson. 



