558 GEOLOGY OF OHIO. 



bent and depressed along the entire length of the posterior hinge line, 

 forming a raised hinge area interiorly on which one or two teeth were 

 probably inserted. 



Avicu'a Whitfieldi, Foerste. 



(Plate 37, Fig. 5.) 



Prof Edward Orton kindly lent tr.e the original specimen from 

 which Hall and Whitfield described their Cypricardites ferrugineum 

 from Todd's Fork, Wilmington, Ohio, in the Paleontology of Ohio, Vol. 

 II. It soon became evident that the gutta-percha cast which the authors 

 had used for s.udy and illustration had been a failure. From a much 

 better cast we have been able to secure a better interpretation of the 

 fossil, though much is yet to be desired as regards our knowledge of the 

 anterior and the posterior extremities of the hinge line. It is evi- 

 dent however that we have here an aviculoid shell. If an Avicula, the 

 name given by its first authors is preoccupied by the Avicula ferruginea 

 of Conrad, and hence a new name, as above, is suggested. Attention is 

 called to the somewhat similar forms published under Avicula subplaim 

 by Hall in the Paleontology of New York, Vol. 2, especially to figure 2 b, 

 on plate 59. 



The valve, the only one so far found, has in general a rather orbicu- 

 loid outline, interrupted of course at the straight hinge line, which it 

 meets posteriorly at a general angle of about 110 degrees. To the best 

 of the writer's judgment the posterior side of the valve was slightly concave 

 before reaching the hinge line, but there is no direct evidence of inaequiv- 

 ocal character that the outline did not continue to be convex as far as 

 the hinge line, as is the case with Leptodomus undulatus for instance. 

 The hinge line posterior to the beak is straight and about 27 mm. long. 

 The beak itself is strongly inclined, and presents a strongly angled and 

 raised, though rounded, upper margin which becomes indistinct at 11 mm. 

 from the tip of the beak. Posteriorly it is defined by a strongly concave 

 area which also soon looses its pronounced character, but which con- 

 tinues obliquely to the posterior end of the shell as a sort of indistinct 

 concave slope between the umbonal ridge and the posterior wing. The 

 umbonal ridge soon disappears into the general rounding of the shell. 

 The anterior third of the shell is but moderately convex or rather flattened 

 except near the margin, especially towards the upper anterior extremity 

 of the shell. The surface of the valve as here described was covered by 

 a series of concentric undulations, quite distinct from each other except 

 on approaching the region anterior to the beak, where they become nar- 

 rower and more like coarse, broad, low strise. At the farthest point to 

 which they can be traced they still show an outline convex towards the 

 ant erior. This point is so near any possible hinge line that it is altogether 

 improbable that a short concave curvature intervened, so as to define an 

 anterior wing. Moreover, the shell is here strongly convex and the last 



