478 PAL-EONTOLOGY OF NEW- YORK. 



Fig. 1 o, 6. View of the npper side of the spire, and of the aperture of a small specimen. 



Pig. 2 a, b. Similar views of a shorter form of the same species. 



Fig. 3. A larger specimen of the same species. 



Fig. 4. A specimen in which the first volution of the spire is concealed. The surface shows 

 some obscure marks of spiral plications. 



Fig. 5. A large specimen in which the last volution is more than usually deflected, standing 

 almost at a right angle with the preceding volution. 



Fig. 6 a, b. Two views of a specimen in which the aperture is obtusely quadrangular. 



Fig. 7 «, 6. A similar specimen to the preceding, where the last volution is less deflected 

 than usual from the direction of the preceding volutions. 



The figures given were intended to be representations of the principal varieties of form 



presented by this species. 



Geological position and locality. In the Oriskany sandstone : Cumberland, Md. 



Plat} ceras ? ( Platyostoma ? ) callosam ( n. s.). 



Plate CXX. Fia. 8 «, b. 



Shell obliquely ovoid, ventricose. Spire consisting of about three volu- 

 tions ; the apex minute, and the first two volutions nearly in the same 

 plane ; the last volution expanding greatly below. Aperture suborbicu- 

 lar ( imperfect in the specimen) : peristome continuous, thickened and 

 coalescing with the body volution at its lower side ; the umbilical cavity 

 closed by a callosity ; the shell, approaching the aperture, becoming 

 lamellose ; the lamellae elevated and imbricating. 



SuKFACE marked by undulating transverse striae and by obscure revolving 



striae, with obsolete parallel undulations. The lines of growth are 



strongly arched forward on the middle of the back of the shell. 



The specimen figured is the only one of the species observed, and, in its 

 characteristic features, is a departure from the typical forms of Platyceras in the 

 expansion of the peristome and its incorporation with the adjacent body volution, 

 forming a thickened callosity, and below this a reliected and thickened pillar lip. 

 Taking the lower half of the aperture, it preserves the character of Platyostoma, 

 but is wanting in an important character shown in the typical species, viz. the 

 joining of the peristome with the body volution near the upper part of the spire j 

 while the columellar lip is irregularly thickened and lamellose. 



Fig. 8 a. View of the back and upper part of the last volution. 



Fig. 8 6. View of the aperture, spire, and callosity of the columellar lip. 



Geological position and locality. In the Oriskany sandstone : Cumberland, Md. 



