EARLY DENOXIC HISTORY OF NEW YORK AND EASTERN NORTH AMERICA igl 



quite abundant, the shell substance is quite generally retained. Early 

 phases of growth are also freely present. 



Of its surface characters we may note that the striae are at all stages 

 fine and round, gradually attaining unequal size by rapid implantation of 

 later striae. Measured along the median line of an average ventral valve 

 these striae number as follows : in a width of 5 mm at 10 mm from the beak, 

 15 ; at 20 mm, 18 ; at 30 mm, 10 ; at 40 mm, 1 1 ; showing a period of rapid 

 increase at medium growth. 



All these fine striae are crossed by minute concentric lines. The 

 cardinal angles in full grown individuals are slightly extended and their 

 cardinal slopes are distinctly crenulated obliquely, the wrinkles converging 

 downward toward the axial line. These however seldom appear in young 

 stages of growth and in some arrested cases may be absent at full size. 

 Over the pallial region in old shells the surface becomes undulated and 

 broadly plicated. 



Of interior characters we may note the relative length of the muscle 

 scars which sometimes extend seven tenths the length of the shell, and over 

 the pallial region the arrangement of a myriad of fine pustules in radial 

 inosculatinor rows. The hinore line is denticulate to its extremities, the 

 denticulations extending" below the hinge marg^in. 



Dimensions. An average specimen has a length of 50 mm and a 

 diameter on the hinge of 70 mm. The largest shell observed is 75 mm in 

 length. 



Localities. Abundant at certain localities in association with C h o n- 

 etes canadensis, near the base of no, 8, Dolbel's brook ; Shiphead, 300 

 feet below lighthouse ; also found loose at Peninsula. So far as observed 

 not associated with L. irene. The species occurs abundantly in the 

 sandy Oriskany shore deposits of central and western New York, but rarely 

 in the calcareous deposits at Becraft mountain. It is also found in the same 

 formation at Cayuga (Schuchert) and Haldimand (Billings), Ontario, and 

 at Cumberland, Md. 



Leptostrophia magnifica van tullia (Billings) 



Plate 37, figures i-6 



S t r o p h o m e n a tullia Billings. Palaeozoic Fossils, v. 2, pt i, 1874, p. 29, pi. 2, 

 jx 6, 6a 



Original description. Shell large, nearly flat, semielliptical, cardinal angles sometimes 

 slightly extended; sides in the posterior half straight or gently concave; anterior hall" 

 broadly rounded; width on the hinge line from one sixth to one fifth greater than the 

 length. 



Ventral valve very slightly convex, most elevated in the middle or a little above, 

 compressed towards the cardinal angles. Area about two lines high at the beak, inclining 

 backwards at an angle of about 45° to the plane of the lateral margin. 



In the interior of the ventral valve the muscular space is subtriangular, rounded in 



