CEPHALOPODA. 255 



Siphuncle slightly excentric, having a diameter at the septa of two mm. 

 where the tube has a diameter of eleven mm. It has not been observed in 

 its passage through the interseptal spaces. 



The test has not been preserved. Surface characters unknown. 



The internal mould is smooth with the exception of the ventral carina. 

 The walls of the chambers sometimes become concave, and occasionally the 

 concavity is shown as a flat, slightly depressed constriction or belt. 



One small fragment has five chambers in the space of thirty-five mm., 

 with a diameter at the larger end of twelve mm. A fragment of the septate 

 portion of a larger individual has ten chambers in the space of sixty-five mm. 



This species is intermediate in its characters between 0. stylus and 0. 

 pravum. It differs from O. stylus in its greater apical angle, generally deeper 

 and more irregular chambers, and the prominent line on the ventrum. Prom 

 O. pravum it is distinguished by the absence of any areolar markings and orna- 

 mentation on the septa. 



Formation and locality. Observed only in the Schoharie grit at Schoharie, N. Y. 



Orthoceras pravum, n. sp. 



PLATES XXXV, FIG. 14 ; XXXVI, FIG. 1 ; I.XXXI, FIGS. 1-8; AND CXI1, FIGS. 15-17. 



Orthoceras tetricum, Hall. Descriptions of New Species of Fossils, etc., p. 45. 1861.  i 



Kift.-oiitli Rep. N. Y. State Cab. Nat. Hist., p. 73. 1862. 

 " " " Illustrations of Devonian Fossils : Cephalopoda, pi. 36, fig. 2. 1876. 



SHELL straight, regularly and gradually enlarging, usually very much distorted 

 from compression. Transverse section circular, often flattened and unsym- 

 metrical. Apical angle about 5°. 



Only a small portion of the chamber of habitation has been observed. 

 This fragment presents no unusual features. Air-chambers regular, deep, 

 varying from eight to fourteen mm. in depth, in the same and in different 

 individuals. 



Septa regularly and deeply concave, the concavity being equal to an arc 

 of 110°. Sutures straight and horizontal, often curved and oblique from 

 distortion. Septa ornamented by a raised lamellose-striate areola around 



