LOWER HELDERBERG ROCKS. 3aO 



Surface marked by fine transverse striae and a few broad shallovir 

 wrinkles. 



This species has some resemblance to the P. ventricosum ; but the ape^^ is more 

 minute, and in that shell the volutions expand regularly and rapidly, while in this 

 one the expansion is more abrupt and the shell more extremely veqtricose. This 

 species shows some transverse wrinkles, which are often preserved in the cast; but 

 this feature has not been observed in P. ventricosum. 



Fig. 1. View of the upper «ide of the spire of a specimen where the apex is entire. The 

 shell is nearly all exfoliated from the body of the specimen. 



Fig. 2. A similar but less symmetrical specimen, preserving little of the shell. 



Fig. 3. Anterior view of fig. 1. 



Fig. 4. View of the upper side of the spire of a smaller specimen, in which the apex is 

 broken off. 



Fig. 5. A smaller specimen of, apparently, the same species, having the apex broken off and 

 the shell compressed from above. 



Geological position and locality. In the upper part of the sbaly linjestone : Scho- 

 harie and Albany counties; Becraft's mountain. 



Platjceras obesuni ( n. s.), 



Plate LXII. Fig. 6 & 7. 



Shell large, elevated hemispheric : apex minute, lq,teral, from which 

 the shell expands abruptly, becoming extremely ventricose in the 

 middle and slightly contracted towards the margin, and again spreading ; 

 aperture campanulate ; peristome sinuate. 



SuEFACE above marked only by fine transverse striae, and towards the 

 aperture bj' short strong flattened plications, upon which the trjinsverse 

 striae are strongly lamellose. 



This species dififers from the P. perlaturn in the proportionally much greater ele- 

 vation, the lateral position of the apex of the spire, and the plicate margin of the 

 aperture. 



Fig. 6. Lateral view of the specimen, from which the shell is nearly all exfoliated. 

 Fig. 7. A portion of the peristome, from which the upper part of the shell has been worn 

 away, showing the plications. 



Geological position and locality. "In the upper part of the shaly limestone at Be- 

 craft's mountain, and in the upper pentamerus limestone near Schoharie. 



[ PALiKONTOLOOY III.] 42 



