EARLY DEVONIC HISTORY OF NEW YORK AND EASTERN NORTH AMERICA 235 



axis 1 infer that they he low in the series. With these were associated 

 the Hmestone blocks bearing P ro ductus c o m o i d e s referred to on 

 page 97. 



Leptocoelia flabellites Conrad 



Plate 29, figures 23-26, 28 



At all localities, specially on the Portage Road, in examples which 

 depart in no measure from the typical forms of the species. 



Spirifer gaspensis Billings 



Plate 31, figures 29-38 



Spirifer gaspensis Billings. Palaeozoic Fossils. 1874, v. 2, pt r, p. 44, pi, 3, 

 fig. 8, a, b 



On'gi/ial description. Shell varying from semicircular to transversely semielliptical, 

 hinge line much extended; often twice the length of the shell; in some specimens shorter, 

 one fourth or only one fifth greater than the length. In the wide specimens the cardinal 

 angles are acute, varying from 40° to 90° sometimes a small portion of the sides, usually 

 about one line in length, at right angles to the hinge; the remainder of the sides, around 

 to the mesial fold of sinus, uniformly and gently rounded. In those with a short hinge, 

 the side, in the upper half of the shell, are straight or slightly concave, and at about 

 90° with the hinge line, the front half rounded. Ventral valve strongly convex, most 

 elevated about the middle of the upper half, or a little above that point; cardinal angles 

 more or less flattened; umbo prominent; beak small, strongly incurved, a well defined 

 mesial depression, concave or subangular in the bottom without ribs, extends from the 

 beak to the front margin where it strongly elevates the edge of the dorsal valve, and, 

 extending the whole width, slightly concave, one or two lines high at the beak. Foramen 

 about three lines wide in a specimen of average size; deltidiura convex, apparently not 

 entirely closing the foramen. Dorsal valve with a strongly elevated mesial fold, without 

 ribs; on each side of the fold moderately convex, compressed near the cardinal angles; 

 umbo and beak curved down to the area, which is small, and apparently nearly in the 

 plane of the margin, but sloping a little outwards. On a side view, the outline of this 

 valve rises, with a more or less abruptly rounded curve, to about one third the length of 

 the valve and then becomes nearly parallel to the lateral margin and continues to the front 

 with a gently convex curve. The front margin, owing to the great elevation of the mesial 

 fold, is nearly squarely truncated, as seen in the side view. 



Surface with from twelve to eighteen simple undivided ribs, on each side of the fold 

 and sinus. These are often crossed by concentric zigzag imbricating lines of growth. 

 In the casts, the ribs vary from acutely angular to rounded angular. AVhen the shell is 

 preserved the ribs are obtusely angular. 



In the casts of the interior (the condition in which the specimens are usually found 

 in the sandstone) the mesial fold of the dorsal valve often exhibits a fine groove along the 

 middle, as if impressed by a thin septum. This is not visible in all the specimens, 

 esi)ecially those that are sliglitly worn. On each side of the umbo of the ventral valve 

 there is (in the casts) a short deep fissure from one to three lines in length. 



Width of a large specimen on the hinge line, twenty-four lines; average width, 

 eighteen lines. The ribs vary slightly in size in different specimens. There are usually 

 five or six in the width of six lines, near to the fold or sinus. The mesial fold and sinus 

 are from four to six lines wide at the front margin. The fold is often elevated six lines at 

 the front. 



