INVERTEBRATE PALEONTOLOGY. 361 



The revolving lines, of which about thirteen to eighteen may be counted 

 on the second whorl, are, when not worn, a little flattened on top, and rather 



regular in size, excepting just below the suture, where they are generally 

 smaller and more crowded. Sometimes, a smaller line is developed in each 

 of the depressions between the others on. the middle and lower part of the 

 last whorl. 



At the time we first described this species, and for some time after, it 

 was supposed to be quite distinct from the form subsequently described by 

 Dr. Evans and Dr. Shumard under the name of Fusus Haydeni ; the latter 

 variety being almost entirely destitute of vertical folds, while that first 

 described by us has them quite strongly developed, not only on the upper 

 turns of the spire, but, in a less degree, even on the body-whorl. It also has 

 a slightly less elevated spire than the variety described by Dr. Evans and 

 Dr. Shumard, being a younger shell. 



Later comparisons of an extensive series of specimens from the same 

 locality and position, have led to the conclusion that no specific distinction 

 can be based on these differences, since the one variety passes by impercepti- 

 ble gradations into the other. In some cases, the volutions seem to be entirely 

 without folds ; while in other specimens, apparently differing in no other 

 respect, they are obscurely developed near the summit of the spire, as shown 

 in figures 1, d, e. Still others have them well developed on nearly all. the 

 volutions, as seen in our figure 1, a, representing the variety first described 

 by us. Generally, however, these vertical folds are entirely wanting on the 

 last aud penultimate whorls. Th.e angle of the spire is also generally from 

 one to three or four degrees greater in young than in adult shells. Again, the 

 plaits on the columella seem to vary in number and distinctness. In one 

 large specimen, like that represented by our figure 1, d, e, by looking tin- 

 around the columella in the aperture, a single, very obscure, oblique plait, 

 can be seen a little below the middle of the aperture ; while, where the spire 

 of the same specimen is broken off at the top of the third volution, the same 

 plait can be seen on the columella, with traces of another above it. Other 

 broken specimens show from three to four of these linear plaits at about the 

 same position. 



As our figures of this species on plate 32 were all drawn, and the plate 

 arranged and engraved before the plaits on the columella had been discovered, 

 none of the broken specimens in a condition to show this character were 

 46 H 



