196 PALAEONTOLOGY OF NEW YORK 



along the centre, the angularity gradually disappearing toward the 

 aperture. Aperture oblique, the shell on the ventral side extending 

 forward in a broadly spatulate expansion, while the dorsal margin is 

 broadly sinuate, the peristome being apparently slightly thickened. Oper- 

 culum unknown. No traces of septa in any part of the body. 

 Surface with some marks of arching transverse striae, which curve towards the 

 aperture on the ventral side, and in the opposite direction upon the dorsal 

 side, or parallel to the margins of the aperture. The ventral side presents 

 two longitudinal depressed lines, which are faintly visible on the surface 

 of the cast. These lines are nearly parallel to the lateral margins, and 

 rather more than one-third of the distance from the margin to the center, 

 but running to the margin a little distance below the apex. 



The typical specimen is represented in figs. 11, 12 and 13. The specimens 

 figured are casts of the interior, the remains of the crystalline substance repre- 

 senting the shell having a thiekness of about one millimetre. 



A single specimen referred to this species is somewhat irregular in its mode 

 of growth, and more attenuate towards the smaller extremity. In many 

 respects this species is similar to what we may suppose to be the young of 

 H. principalis ; but that species is proportionally narrower in its upper part, and 

 more abruptly expanding below. 



Formation and localities. In the Schoharie grit at Schoharie, and in the upper 

 part of the limestone at Clarence Hollow, in Erie county, N. Y. 



Hyolithes principalis. 



PLATE XXXII, FIGS. 17-21. 

 Hyolitheg principalis. Hall. Illustrations of Devonian Fossils : Pteropoda, pi. 27, figs. 17-20. 1876. 



Form an elongated triangular pyramid, which is slightly curving towards the 

 dorsal side, apparently more abruptly expanding towards the aperture 

 than in the upper part. A transverse section below the middle of the 

 length is semi-elliptical, with a width twice and a half as great as the 

 height; the lateral angles moderately acute. Ventral face gently convex 



