96 PALEONTOLOGY OP OHIO. 



Orthodesma PARALLELA. 



Orthonota parallela, Hall; Pal. N. Y., Vol. I., p. 399, pi. 82, flgs. 7a and d. 

 The specimen represented by the figures 7a and d, loc. cit, was ob- 

 tained many years ago among fossils collected at Cincinnati, Ohio. It 

 is an internal cast in a calcareous sandstone, and was referred to the 

 above species from its similarity of form in the absence of external char- 

 acters. On strict comparison with the New York specimens, one of 

 which is represented by fig. 7c of the same plate, and another by fig. 76, 

 there are certain features that would seem to indicate it as belonging to 

 quite a distinct species. The umbonal ridge is strongly marked and sub- 

 angular, and the flattening of the sides of the shell, as well as the greater 

 gibbosity of the valves, could never have existed on a shell specifically 

 identical with that represented by fig. 1c. Prom the character of the 

 rock composing the cast, and from the uncertainty of its exact locality, 

 there may possibly be some doubt of its geological position ; and for these 

 reasons we prefer to leave it without specific name until other and 

 authentic specimens shall be obtained. 



Orthodesma contracta. 



Plate 2, flgs. 4, 5. 

 Orthmota contrada, Hall ; Pal. N. Y., Vol. I., p. 300, pi. 82, flg. 8. 



Shell small, elongate trapezoidal, length twice and a half to three 

 times the width; cardinal and basal margins sub- parallel ; hinge line 

 exceeding half the length of the shell, straight posterior to the beaks; 

 posterior end obliquely truncate, scarcely rounded on the margin ; basal 

 line straight or gently sinuate near the middle ; anterior end contracted 

 beneath the beaks to a little more than half the width of the body of the 

 shell, and extended anteriorly to a distance equal to its width ; extrem- 

 ity sharply rounded ; beaks small, incurved, flattened on the umbones, 

 and projecting a little above the line of the hinge ; umbonal ridge prom- 

 inent and sub angular ; cardinal slope flattened, or slightly concave. 



Surface of the shell marked by fine, irregular, concentric lines, and by 

 stronger, distant undulations, or varices, marking stages of growth, and 

 also on the cardinal slope by several strong, equi-distant, oblique plica- 

 tions parallel with the posterior extremity of the shell, extending from 



