LOWER HELDERBERG ROCKS. 330 



Pleurotoniaria labrosa ( n. s.)- 



Plate LXVL Fio. 1 - 5 ; and Plate LVII. Flo. 6 a, 6. 



Shell rhomboid-ovate. Spire little elevated above the body of the shell : 

 volutions three or four ; the upper ones small and moderately increasing} 

 the last one ventricose, much expanded on the outer side, and subangu- 

 lar : aperture broadly ovate ; the columellar lip extremely thickened, 

 the callosity extending to the outer lip. 



Surface marked by prominent spiral ridges with wider furrows between, 

 and, on the upper part of the volution, by a broader band or groove j 

 which is margined by carinae : lines of growth marked by strong ele- 

 vated lamellose striae, which are undulated in passing over the spiral 

 ridges ; those marking the broader spiral band are less strongly ele- 

 vated, and make a single retral curve, indicating the marginal sinus. 



The entire surface has a reticulated aspect; the spiral ridges being equidistant, 

 while the lamelliform strise of growth are often irregular. In different degrees of 

 exfoliation, the surface presents some variety of aspect, some of the lines remaining 

 on the cast. The specimens figured are all distorted to a greater or less degree. 



This species resembles very closely the P. balleata of Phillips, a species from the 

 Wenlock limestone. 



Fig. 1 a. An imperfect specimen from the Shaly limestone. 



Fig. 1 b. An colargement of the surface of the same. 



Fig. 2 o. A cast of the same species ! view of the aperture, which is filled with stone. 



Fig. 2 5. View of the exterior of the specimen. 



Fig. 3 a. The exterior of a specimen where the shell is mostly removed, showing the spiral 



band and the sinuosity in the peristome. 

 Fig. 3 6. View of the aperture of the same, showing the thickened columellar lip; 

 Fig. 3 c. An enlargement of the surface markings. 

 Fig. 4 a, b. Two views of another individual, showing in one of the figures the thickened 



lip, which, on the upper side, extends as far as the marginal sinus. 

 Fig. 5 a, b. Two views of a crushed specimen, showing in one of the figures the externally 



thickened columellar lip. 



The same species is illustrated in fig. 6 a b, Plate lvii. 



Geological position and locality. In the upper pentamerus limestone : Carlisle and 

 Schoharie, Schoharie county; and a single specimen in the shaly limestone at the 

 base of the Helderberg mountains, Albany county. 



