CEPHALOPODA. 277 



Tire specimens embraced in this variety and in the species as above consti- 

 tuted are all very imperfect. Those from the quarries at Ithaca, N. Y., show 

 considerable variation, although occurring in the same association. This varia- 

 tion is principally owing to the conditions of preservation. The specimens 

 are nearly all very much compressed, and the important specific characters 

 obscured. The individuals from the Hamilton group exhibit very similar con- 

 ditions, rendering a separation and specific distinction of the two forms impos- 

 sible without more perfect material. 



Formation and locality. In the lower members of the Chemung group, in the 

 quarries about Ithaca, and at Cortland, Cortland county, N. Y. 



Orthoceeas linteum, n. sp. 



PLATE LXXXVII, FIGS. 3,4. 



A portion of the chamber of habitation, and the last air-chamber of an indi- 

 vidual, is recognized as a distinct species, on account of the decided character 

 of the surface ornamentation. The tube is much compressed and without 

 any evidences as to the transverse section, the concavity of the septa, or the 

 elements and position of the siphuncle. 



The chamber of habitation, so far as observed, shows no evidences of a 

 constriction, or a departure from the general contour of the tube. The last 

 air-chamber has a depth of seven mm. • 



The test has been dissolved. The surface-markings, as shown on the 

 internal mould, are very fine, sharp, regular, longitudinal striae, of which 

 there are fourteen in the space of three mm., crossed by equally regular, 

 sharp, transverse striae. 



This species, in external form, somewhat resembles 0. Bebryx; but the sur- 

 face characters are very distinctive. 



Formation and locality. In the Hamilton group, Leonardsville, Madison 

 county, N. Y. 



