334^ PALiEONTOLOGY OF NEW- YORK. 



The three following species are straight, or slightly arcuate at the 

 apex, but without volutions. 



Platyceras plicatuiu. 



Plats LXIV. Fia. 1-5. 

 Calaola pttcata : CojfiUD, Annual Report on the PalsBontology of New- York, 1840, p. 207. 



Shell obliquely conical, not incurved 1 apex acute sublateral, expanding 

 and becoming ventricose below : aperture rounded, oblique ; peristome 

 regularly sinuate on the right side, shorter and plain or broadly sinuate 

 on the left side. 



Surface cancellated by transverse lamellose striae, and by longitudinal 

 rounded or threadlike striae : one side regularly marked by broad 

 rounded plications which originate at one-third or one-half the distance 

 from beak to base. 



This species varies but little in its general form, being sometimes a little more 

 slender. The plications are more strongly developed in some of the specimens than 

 in others, and the plicated side is always more extended; the shorter side of the 

 aperture sometimes showing one or two broad undulations. 



Mr. Conrad described the Calceola plicata as follows : " Shell longitudinally 

 " striated ; plicated towards the aperture, the margin of which is waved." The 

 original specimen labelled by Mr. Conrad leaves no doubt of the species to which 

 this name was applied. 



Fig. 1. A young specimen in which no plications are developed. ' 



Fig. 2. A more slender specimen in which the plications are strongly marked. 



Fig. 3 & 4. A larger individual, in which the plications are but moderately developed. 



Fig. 5. A large specimen which is compressed) the view showing a width greater than the 

 natural width of the shell. 



Geological position and locality. In the shaly limestone of the Lower Helderberg 

 group : Albany and Schoharie counties. 



