G8 BULLETIN OF THE 



valve, — a feature in which this species differs from its representatives. — 

 Junction Cliff, Anticosti. 



Atrypa Dalman. 

 Atrypa impressa Shaler. 



Sy.v. Atrypa reticularis Billings. 



Outline of shell obscurely quadrate, sometimes rather sub-orbicular ; 

 about as broad as high ; diameter from valve to valve about one half the 

 distance from beak to border; valves nearly equally convex, toothed valve 

 usually a little the greater; hinge-line straight, nearly as great as width of 

 shell. Tooth-valve rather convex, side slopes more abrupt than central, 

 slightly flattened or depressed opposite the hinge-line. Point of greatest 

 convexity at one third the distance from beak to border. Umbo projecting 

 above the hinge-line about one ninth the distance from beak to border; 

 laterally compressed ; recurved ; projecting beyond the hinge-line ; beak 

 minute, pointed, distinct. Socket-valve evenly convex ; most projecting 

 point a little nearer the hinge-line than border. Originating at the beak 

 there is a distinct, rather abruptly depressed mesial furrow, which grows 

 more shallow towards the centre of valve. Radii branching twice from 

 beak to border, a little larger in the centre of valve than on the border. 



The adult condition of this species differs strikingly from any other form 

 included under the name of Atrypa reticularis. — Near Southwest Point, 

 Anticosti. 



Atrypa flabella Shaler. 



Outline sub-orbicular ; transverse diameter about one fifth greater than 

 from beak to border; the slopes on either side of the beak form an angle 

 of about 1 50° at the valve. Toothed valve convex ; rather ridge-like in the 

 centre; depressed on the border opposite the beak; slightly compressed 

 near the umbo; most, convex point one third the distance from beak to 

 border; beak not distinct from hinge-line. Socket-valve slightly convex ; 

 a distinct mesial impression divides the surface into two lobes. Surface with 

 from twelve to eighteen rounded, club-shaped, radial ridges. Near the 

 border of some large specimens there are a few concentric, imbricating 

 lines of growth. 



It is not unlikely that this form Ls specifically identical with the A. hemi- 

 apJierica IIai.l, from the Clinton of New York. There are several points 

 of difference between this form and the A. hemispherka Murch. — Near 

 Sunt Invest Point, Anticosti, upper part of Division E, Canada Geological 

 Survey. 



Rhyneonella Fischer. 

 Rhynconella fringilla Billings. New Species of Low. Sil. Fossils; Can. 

 Geol. Sur., 1862, p. 141, Fig. 118. — Near Gull Cape, Anticosti. 



