GO BULLETIN OF THE 



closer approximation of the brachial supports of the socket-valve, and k-ss 

 length of the adductor impressions in the same valve. — Southwest Point, 

 Anticosti. 



Orthis anticostiensis Siialer. 



Syn. Orthis porcaia Billings (non McCoy), Can. Geol. Sur., 18C2, 

 p. 135. — Ellis Bay. 



Orthis cequivalva Shaleb. 



Syn. Orthis hybrida Billings. 



Shell somewhat lenticular; one fifth wider than from beak io bo. Jc; 

 valves nearly equal in convexity; toothed valve a little the most prom- 

 inent; hinge-line rather more than half the width of shell. Toot he J valve 

 strongly evenl}' convex, a little depressed opposite the umbo; umbo rising 

 above the hinge-line about one sixth the distance from Leak to border, a 

 little laterally compressed; beak minute, scarcely projecting b>_\o-id the 

 hinge-line, a little recurved ; area about twice as wide as that of socket- 

 valve ; width one sixth of length; steeply sloping; most convex point of 

 valve a little nearer the beak than border. Socket-valve nci'v evenly 

 convex; very slight mesial depression, extending from the i.rabo to the 

 centre of valve, where it fades out, and is succeeded by a slight ridge, which 

 extends to the border, beak distinct ; not rising as far above the hinge-line 

 as that of opposite valve by the width of socket-valve area. Surface with 

 fine dichotomous stria?, with interspaces as wide as the ridgtfl. — Junction 

 Cliff, west end of Anticosti. 



Orthis rhynconelliformis Siialeu. 



Form varying from sub-circular to pentagonal ; usually with the transverse 

 one fill li greater than the diameter from beak to border; hinge-line very 

 short, scarcely one half the width of shell. Toothed valve n.oderately con- 

 vex, with a very broad, shallow mesial sinus beginning near the centre, and 

 rapidly widening to the border; umbo somewhat laterally compressed; 

 rising above the hinge-line; acutely pointed ; not recurved; beak minute, 

 very distinct. Socket-valve evenly convex ; highest point near the middle 

 of valve; usually a faint mesial sinus near the beak, fading out in the centre 

 of the shell. Fissure of toothed valve wider than lomr, sides curved ; teeth 

 small, laterally compressed ; muscular impressions extending to or beyond 

 the middle of valve, very lobatc ; lobes pointed. 



Surface with numerous angular radii; bifurcating twice from beak to 

 border; about four in the space of one line on the centre of border: inter- 

 spaces about as wide as ridges.— Gull Cove, eastern end of Anticosti. 



Orthis alata Sum. Kit. 



Shell nearly semi-oval, sometimes slightly quadrate; hinge-line a little 



