490 PALAEONTOLOGY OF NEW- YORK. 



Pliolidops 8i|uaiiiifoi'iiiis (Hall). 



Plate CIII B. Fia. 6 a, b. 



Orbiculu squamiformis : Report of the Fourth Geological District, 1843, pag. 108, fig. 1. 

 — — Palieontology of New-York, Vol. ii, pa. 250, pi. 93, f. 4 a, b. 



Shbll oval or subquadrate oval, very depressed : apex excentric. Surface 

 marked by strong concentric lamellae, which are close together on the 

 anterior, but wider and diverging on the posterior part of the shell. 

 Shell thin, translucent. Fine radiating striae cross the lamellae in well 

 preserved specimens. 



Fig. 6 a. Interior of a specimen of the natural size. Fig. 6 b. The aame enlarged. 

 For the exterior of the shell, see Plate liii, vol. 2, 



Geological position and locality. In the shale of the Niagara group : Lockport, 

 Rochester, and Sweden, New- York. 



Pliolidops ovatus (n.s.). 



Plate CIII B. Fio. 7 a, b. 



Shell ovate : apex excentric. Surface marked by fine concentric lamellae 

 of growth, which are wider on the posterior part of the shell. Very 

 minute radiating striae are sometimes visible. 



This shell resembles the Niagara species; but the lamellose striae are finer and 

 more closely arranged, and the shell is often proportionally broader. 



Fig. 7 a. Exterior of a specimen of the natural size. Fig. 7 b. The same enlarged. 



Geological position and locality. In the shaly limestone of the Helderberg group: 

 Albany county. 



Pliolidops teriiiiiialis ( n. s.). 



Plate CIII B. Fio. 8 a, b, r, d. 



Shell subelliptical, broader behind, and narrowing to the apex : apex 

 terminal. Surface marked by strong squamiform lamellae : a flattened 

 subtriangular space beneath the apex ; the inner margins of the shell 



