296 Systematic Paleontology — Middle Devonian 



Collections. — Maryland Geological Survey; Xew York State Museum; 

 American ^Museum of Xatural History. 



Superfamily TAENIOGLOSSA 

 Family CAPULIDAE 



Genus PLATYCERAS Conrad 



Platyoeeas eeectum Hall ( ?) 

 Plate XXXVII, Figs. 1-3 



Acroculia erecta Hall, 1S43, Geol. N. Y., pt. iv, p. 174, fig. 6 on p. 172. 



Platyceras erectum Hall, 1861, Descriptions of New Species of Fossils, p. 4. 



Platyceras erectum Hall, 1862, Fifteenth Rep. N. Y. State Cab. Nat. Hist., 

 p. 32. 



Platyceras erectum Hall, 1876, Illustrations of Devonian Fossils: Gastero- 

 poda, pi. ii. 



Platyceras erectum Hall, 1879, Pal. N. Y., vol. v, pt. ii, p. 5, pi. ii, figs. 4-11. 



Platyceras erectum Clarke, 1903, N. Y. State Mus., Bull. 65. p. 549. 



Platyceras erectmn Grabau and Shimer, 1909, N. Am. Index Fossils, vol. i, 

 p. 683, fig. 963a. 



Description. — Shell regularly arcuate to the inrolled spire; nearly two 

 volutions; the spire at the apex closely inrolled for about one and one-half 

 volutions beyond which the body volution expands somewbat rapidly ; tbe 

 aperture often spreading, not infrequently oblique with a sinuate peri- 

 stome. Surface marked by closely arranged, revolving, lamellose striae, 

 which, upon the lower half of the body volution, are abruptly arched 

 along narrow bands, corresponding with former sinuosities of the aperture. 



The collection contains several exfoliated and essentially smooth speci- 

 mens which agree more nearly with this species than any other. The 

 margins are very imperfectly shown but there are radiating bands or 

 ridges shown on the lower part of the body volution of two specimens. 

 The specimens were sent to Dr. Grabau with the question whether he 

 would agree in referring them to P. erect'um and he answered as follows : 

 " That is as close as you can get I think. Each individual of Platyceras 

 represents a distinct mutation, no two being exactly alike." Dr. Grabau 

 has called attention to the difficulties attending the systematic study of 



