THE NAUTILUS. 113 



but slightly modified, however, by the carina?. The nepionic whorl 

 is smooth, or very slightly and irregularly roughened or pitted; this 

 perhaps may be the result of incipient erosion. Below this, the 

 lines of growth on the second and third whorls are strong, straight 

 and quite regular, and intersecting these are numerous stronger, 

 parallel, revolving striae, which give a reticulated appearance to the 

 surface ; on the fourth whorl the revolving lines sensibly diminish 

 in strength and towards the aperture become subobsolete. This 

 sculpture is uniformly present and is apparently characteristic of the 

 bicarinate form. The persistence of the revolving lines varies in 

 different individuals. Usually they fade out as the shell assumes 

 the globose form, but occasionally continue until the shell is nearly 

 mature. 



There is considerable variation in the height of the apical whorls. 

 Most of the specimens in the bicarinate stage are more depressed 

 than the type and the carina is less prominent on the superior whorls. 

 Fig. 2 is the most depressed individual seen, and the spire is wholly 

 flattened with no projection of the carina above the body whorl. 

 As the shell increases in size, the superior carina becomes less 

 prominent, the lip of the lower whorl rises and gradually passes over 

 its edge, and, thenceforth, the shallow suture characteristic of the 

 mature shell is maintained. Erosion begins, the acute spire and, 

 generally, all the sculptured whorls disappear, and the shell assumes 

 the characteristic globular shape of maturity. 



During this stage, the carina? progressively diminish in strength 

 and become mere angles and finally disappear. The groove between 

 them widens and becomes plane and persists in the half-grown and 

 mature shells as the characteristic flattening of the body whorl. 

 The superior carina is the less persistent and completely disappears 

 in the regularly rounded curve of the upper part of the whorl. The 

 lower carina and the resulting angle remain longer in evidence and 

 cause in the mature shell the greater width of the lower part of the 

 body whorl. The carina? persist longer in the more conical speci- 

 mens (Fig. 4) than in the depressed individuals (Fig. 3). For 

 comparison with this stage in the Florence series, the smallest ex- 

 ample seen from the Falls of Ohio is figured (Fig. 5). It measures 

 5.5x5.5 mm. The apical whorls are somewhat eroded, but enough 

 is left to show that they were carinate and had the characteristic 

 sculpture ascribed to cincinnatiensis. They are more depressed 



