NIAGARA GROTTF. 289 



652. 2. ACROCULIA ANGULATA (n. sp.)- 



PL. LX. Fig.ia-d. 



Apex attenuated, involute, forming one or two minute volutions, below wliich the shell ex- 

 tends in a broad curs'e, expanding rapidly towards the aperture which is much dilated ; surface 

 angulated, a sharp carina on the upper and lower outer margin of the volution, an obtuse carina 

 on the middle of the back, and the inner margins angulated ; transverse section unequally 

 pentangular ; surface finely striated ; striae undulating over the surface, arching upwards on 

 the sides, and downward or towards the aperture between the outer angles and the central 

 carina, upon which they are twice undulated or bent. 



This species will be readily recognized by its angular form, which is always more or less 

 perfectly defined. In many specimens the apex does not form visible convolutions, and in 

 others there is sometimes a distinct volution of the larger part of the apex, so that the margin 

 of the aperture is brought in contact with the upper part of the shell. There is likewise con- 

 siderable variation in the degree of obliquity of the partial spire. 



Fig. 4 a. The back of a small specimen, v>fhere the shell is scarcely preserved. 

 Fig. 4 b. Upper side of the same. 



Fig-. 4 c. Back of another specimen, where the angles, carina, and surface striae are well preserved. 

 Fig. 4 d. Upper side of the same, showing in part the expanded aperture and the minute volu- 

 tions of the attenuated apex. 



Position and locality. In the shale at Lockport. A single specimen (very similar to this 

 species, and perhaps only a variety of the same, forming a single volution nearly in the same 

 plane) has been found in ,the upper limestone of the Clinton group at Lockport. 



[ Paleontology — Vol. h.] 37 



