GASTEROPODA, PTEROPODA AND CEPHALOPODA 



OF THE 



UPPER HELDERBERG, HAMILTON, PORTAGE AND CHEMUNG GROUPS. 



GASTEROPODA. 



PLATYCERAS, Conrad. 

 Platyceras (Orthonychia) subrectum. 



PLATE I, FIGS. 1, 2. 



(trthniiyrhla Hali,. Geology of N. Y. Surv. Fourth Geolog. Dist., p. 172, f. 3. 1843. 

 Pi"t i/ceras subrectum Hall. Twelfth Rep. N. Y. State Cab. Nat. Hist., p. 18, fig. 1859. 

 Platyceras (Orthonychia) subrectum Hall. Descriptions of New Species of Fossils, etc., p. 1. 1861.* 



Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 29. 1862. 

 " " Hlustration8 of Devonian Fossils: Gasteropoda, pi. 1. 1876. 



Shell unguiform, elongate, subspiral, making not more than a quarter of a 

 volution in the length of three-fourths of an inch, below which it is entirely 

 straight. Apex minute, abruptly incurved, solid, nearly cylindrical, for a 

 short distance below the apex, and gradually compressed, becoming a little 

 concave on the posterior side. Aperture somewhat oblique. 



Surface marked by concentric striae, which are sometimes crowded together, 

 forming ridges or wrinkles. 



* Contributions to Palaeontology. Continuation of Appendix C [of the 14th Rep. State Cab. Nat. Hist., 

 published .Inly, 1861]. Descriptions of New Species of Fossils, from the Upper Helderberg, Hamilton and 

 Chemung Ghroups, Albany, 1861. Pages 1-24 of this paper were printed and distributed in August, 1861, and 

 the remaining portion, pp. 25-84, in September, 1861, according to the imprint at the bottom of each page. 

 It is included in the Fifteenth Report on the State Cabinet of Natural History (pp. 26-112) together with 

 illustrations of species therein described (on Plates 4-10) and accompanying explanations of figures. 



