440 VM..KOSTOLOGY OF NEW YORK. 



Siphuncle close to the ventral margin ; its characters not determined. 



Test thin, and only partially preserved on the specimens examined. 

 Surface marked hy stria? of growth, which are essentially parallel to the 

 direction of»the septa; the striae on the inner volutions are sometimes 

 crowded into fascicles, making slightly elevated ridges. The sinus, inferring 

 from the direction of the striae on the periphery, has been deep, abrupt at the 

 sides, and gently curving in the bottom. 



The internal mould is essentially smooth, preserving some marks of the 

 external striae, and having the suture lines moderately impressed. The 

 individuals of the species, judging from a few fragmentary specimens, have 

 had a diameter of at least 100 mm., and probably more. The specimen 

 figured on plate 71 has a diameter of thirty-eight mm., and is only a portion 

 of the chambered part of the shell. Another imperfect specimen, preserving 

 a part of the chamber of habitation to the length of about forty mm., has 

 a diameter, at the last air-chamber, of thirty two mm. ; the depth of the 

 chamber being six mm. 



This species closely resembles G. Vanuxemi in most of its characters. A 

 specimen, preserving a portion of the chamber of habitation and several attached 

 air-chambers, when compared with a portion of the tube of the same size, in 

 three specimens of G. Vanuxemi, shows a difference in the depth of the air- 

 chambers, nearly as six to ten : the outer ones in the fragments of G. unilo- 

 batus measuring but 5.5 mm. It is possible however, that these forms may 

 prove to be identical when large collections shall be compared, and that the 

 differences noted may be due to influences of the surrounding physical condi- 

 tions during their existence. At present there are but few specimens of this 

 species known, and these occur in a compressed and distorted condition. 



Formation and locality. In the fissile shales of the Hamilton group, on the 

 shore of Cayuga lake. 



