66 NEW YORK STATE MUSEUM 



form specimen of the internal cast, showing in part the rounded whorls, 

 1 1 or 12 in number, and partly exposing the inner surface of the whorls. 

 At the same time he applied the name M. macrospira to an external 

 mold of moderately large size and of similar angle to M. 1 o g a n i i but pre- 

 senting whorls simply and rather sharply angulated by the peripheral slit 

 band. It has been questioned by Whiteaves whether any distinction 

 between such bodies can or should be made. On consideration of the 

 material representing these shells in the Rochester and Shelby collections, 

 in most cases clear cut internal casts present rounded whorls save in the 

 mature growth of the shell, such casts of the later volutions preserving the 

 angularity at the periphery. At times however this obscurity of angulation 

 on the cast is manifested on all whorls. It therefore seems probable that 

 but a single species is represented by these two names, and of these it is 

 M. macrospira which should be employed, as this is the name given to 

 the external mold on which the species characters are best expressed. The 

 species is represented by a number of specimens from Rochester, a large 

 example from the upper Shelby dolomite and several small specimens from 

 the lower horizon. 



The illustrations here given show the angularity of the lower whorls, 

 on which the slit band stands out prominently at the periphery, being nar- 

 rowly convex, with elevated, thin margin not rising to the hight of the sur- 

 face of the band. Of the whorls, which may be 10 in number, the last four 

 show this angularity with increasing distinctness, but the earlier whorls 

 even when well preserved present only a rounded surface. The slit band 

 lies almost centrally on the whorl, but the overlap by later growth makes it 

 appear below the middle except on the final whorl. The slope on the upper 

 part of the whorl to the slit band is more direct and less convex than below. 

 The concentric surface lines slope directly backward about the periphery 

 but show a curvature on the umbilical surface. The apical angle is from 

 20 to 25. The direction of the suture is quite transverse ; form of 

 aperture not observed. Umbilicus narrow but open to the apex of the 

 shell. 



