42 



Length of a full grown shell usually about two and a half inches ; width, 

 twelve to fifteen lines. Sometimes the depth of the two valves together 

 is greater than the width. The shell is often more or less compressed later- 

 ally, and exhibits distortions, which are natural, or not the result of 

 pressure. 



Locality and Formation. — Indian Cove and Grand Greve, Gasp^. Very 

 abundant in the Gaspd limestone, Div. 8, also in the Gasp^ sandstone, 

 and at Perce. 



Collectors,— ^iv W. E. Logan, Prof. J. W. Dawson and R. Bell. 

 Leptoccelia flabellites. (Conrad.) 



Plate 3, figs. 5, 5a, 5^», 6, 6a, 

 Atrypa flabellites. Conrad, Ann. Rep.,*] 841, p. 55. 

 Leptoccelia flabellites. Hall, Pal. N.Y., vol. 3, p. 449, pi. 103, 1C6. 



Description.— -Ovsite, sometimes nearly circular ; apical angle varying 

 from about 120*^ to 170° y cardinal edge either straight or gently convex, 

 often slightly concave close to the beak ; sides varying from gently to 

 strongly rounded ; front usually somewhat straight or slightly concave or 

 convex in the middle third. Ventral valve moderately convex, most 

 elevated a little above the mid-length. The mesial depression usually 

 dies out at one-half or two-thirds the length, sometimes runs nearly to 

 the beak, as in fig. 5. It has a single rib which extends from the beak 

 to the middle of the front margin. There is usually a large rib, more 

 prominent than any of the others, on each side of the mesial depression. 

 From these large ribs, the shell descends with a flat, slightly concave, 

 or slightly convex, slope to the margin. In some specimens the mesial 

 depression is scarcely perceptible. Beak small, incurved down to the 

 plane of the lateral margin, but not in contact with the dorsal umbo. 

 Dorsal valve gently convex or nearly flat. In the upper half there is 

 usually a slight mesial depression extending from the beak about half the 

 length of the shell. Two of the ribs, one on each side of the mesial line, 

 are larger than the others, and at the front are more or less elevated, 

 forming an obscure mesial fold, which dies out about the mid-length of the 

 shell. On each side of the fold the shell is often more or less convex, 

 generally with a strong curve down to the margin around the front and 

 part of the sides. The place of the umbo is nearly flat, with exception 

 of the slight mesial depression above noticed. 



The number of the ribs is slightly variable. In general the ventral 

 valve has a single median rib, smaller than the others, and situated in the 

 mesial depression. On each side, there are four or five well developed 



