PLATE 60. 



Fig. 1. 649. 2. Platyoptoma niagakensis. ( Pag. 287.) 



1 a, b, c. Young individuals, where tiie spire is depressed as low as the outer volution. 



1 d. An individual having the spire equally depressed, and the surface couspicuouslj marked by longitudinal 



strias. 

 1 /. A small specimen having an elevated spire, with the surface marked as in fig. 1 d. 

 1 g. View looking on the spire of a similar specimen. 

 1 ft. A small specimen having the spire much elevated, and the volutions longitudinally and transversely 



striated. 

 1 i, k, I. Back, summit and front views of a globose specimen preserving its natural proportions. 

 1 m, n. Two views of a similar specimen, tiaving the aperture somewhat more expanded. 

 1 o, p. Two views of a larger individual with an expanded aperture and a strong fold upon the back of the 



volution, and a sinus in the margin of the aperture. 

 1 r. A similar larger specimen. 

 1 s, t. View of spire, and partial front view of a large specimen from which the shell is partially exfoliated. 



1 M, V. View of the summit of two other individuals having the usual depressed spire of this species. 



Fig. 2. 650. 3. Platyostoma hemispherica. ( Pag. 2S8.) 



2 a. View of the summit. 



2 b. Front view. The shell is so much depressed, that the figures can give no true idea of the aperture. 



Fig. 3. 651. 1. AcRocuLiA niagakensis, ( Pag. 2S8.) 



Fig. 4. 652. 2. AcRocuLiA angulata. (Pag. 289.) 



4 a. The back of a small specimen, where the shell is scarcely preserved. 

 4 6. Upper side of the same. 



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

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

 tenuated apex. 



