204 PALEONTOLOGY OF NEW YORK. 



internal structure are distinctive features, as compared with other species in 

 the same formation. The substance of the shell has been comparatively thin, 

 and apparently hyaline, and from its mode of preservation, as well as from its 

 peculiar form and characters, it may be inferred that the fossil belongs to the 

 Pteropoda. The genus proposed for its reception may be characterized as 

 follows : 



Fossil an obliquely conical tube or sheath, expanding from the apex more 

 rapidly on one side, while the other maintains a nearly vertical line; 

 the interior crossed by arching septal lines, which are unsymmetrical on 

 the two sides of the axis or summit of the arch, and on the shorter side 

 are recurved near their junction with the exterior shell ; the septa crossed 

 by longitudinal lines, which apparently penetrate the cavity, and give a 

 cancellated aspect to the interior. Shell thin, translucent, and marked by 

 lamellose lines of growth, subparallel to the septal lines. Aperture and 

 complete form of shell unknown. 



CLATHR0CO2LIA eborica, n. sp. 



PLATE XXXU, FIG. 10; AND PLATE XXXII A, FIGS. 28, 29. 



The figures illustrate the only known form of the genus above described. 



The length of one specimen is over forty-six millimetres, and the apex is 

 incomplete. The greatest width at the aperture, measured in a directly trans- 

 verse line, is about twelve millimetres. 



Formation and localities. In the calcareous shale of the Hamilton group, east 

 of Alden, Erie county, N. Y. ; and in a calcareous band in the same shales, 

 at Darien, Genesee county, N. Y. 



