NATURAL SCIENCES OP PHILADELPHIA. 171 



A'oluine of the Palaeontology of New York, from the Oriskany 

 Sandstone, under the name Cyrtolites e^^9a>i8M8, excepting that its 

 apex is not so alternate. Although possibh^ not a true PlaUjceraii^ 

 it seems to be more nearly- allied to the section of the same for 

 which the name Orthonychia has been proposed than to Cyrtolites^ 

 which was founded on a very different type (C. o?'nafiis, Con.), 

 with a very peculiar style of ornamentation. In its surface mark- 

 ings our shell agrees with Plafycei-as, in being merely marked 

 with fine lines of growth more or less undulated on the anterior 

 slope, with traces of very obscure radiating stripe, which latter, 

 with its non-spiral form, indicate relations to the section Ortho- 

 nychia. It therefore bears the same relations to the elongated 

 forms of Orthonychia that the depressed, rapid!}- expanded species 

 of Platyceras, such as P. obscurum, bear to the typical forms of 

 the genus. 



Locality and x^osition. Lodi, Ohio. Waverley group of the 

 Lower Carboniferous series. 



PLATYCERAS TORTUM, Meek. 



Shell very thin, dextral, attaining a medium size ; in young- 

 specimens composed of about one and a half to two volutions 

 subglobose, these first turns being contiguous, rounded and rapidly 

 increasing in size, after which the next turn, which composes the 

 larger part of the shell, becomes free, very oblique, and increases 

 little in size toward the aperture, thus making the entire form 

 very obliquel}^ subrhombic; body volution a little flattened on 

 the upper slope, subangular above, and somewhat prominently 

 rounded near and below the middle ; aperture apparently oval 

 suborbicular ; lip without sinus ; surface without plications, and 

 with only moderately distinct lines of growth. 



Length, 1.3G inches; breadth, 1 inch; breadth of aperture, 0.80 

 inch; height of aperture, 0.82 inch. 



I have long been familiar with casts of this shell in the collec- 

 tions of the Illinois Survey-, but as they were only casts of the 

 interior, I had some doubts whether they might not be from dis- 

 torted specimens of some of the other Gasteropoda already de- 

 scribed. The specimens from which the above description was 

 made out, however, retain the shell itself, and show that it is a 

 true Platyceras. Specifically it is more nearly allied to some of 

 1871.] 



