LOWER HELDERBERG ROCKS. 
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Platyceras Irisulcatum (n. s.). 
Plate LX. Fig. 6 d , e. 
Shell obliquely and very depressed-subconical : apex consisting of one 
or two small volutions, which are free from pb cations and slightly 
ob ique; last volution free, abruptly expanding and becoming ventri- 
cose towards the aperture : aperture round; peristome sinuate, some¬ 
what reflexed. 
Surface, on the upper or right side of the body-volution, marked by two 
strong longitudinal furrows, which divide that side of the shell into 
three broad lobes or plications, the opposite side being obscurely plicate; 
transversely marked by lamellose striae, which are abruptly undulated 
on the depressions and elevations of the surface, and obscurely marked 
by fine longitudinal striae. 
The first volution is broken off in the specimen figured, and the aperture a little 
distorted by pressure. 
Fig. 6 d. View of the upper side of the spire, showing the two sharp grooves and the broad 
lobes. 
Fig. 6 e. The left side, showing the sinuous striae with an undefined longitudinal plication : 
there are, besides this, one or two obscure plications. 
Geological position and locality. In the shaly limestone of the Lower Helderberg 
group : Schoharie county. 
Platyceras piieiforine (n. s.). 
Plate LXI. Fig. 3 a , b. 
Shell very depressed-conical or hemispheric : apex subcentral, consisting 
of a single minute volution, from which the surface slopes almost 
equally on all sides to the margin : aperture nearly round ; peristome 
sinuous. 
Surface longitudinally plicated; plications broader below, and scarcely 
reaching to the apex : a few pustulose markings on the sides and near 
the apex; concentrically striated by fine closely arranged striee. 
