INSTITUTE OF SCIENCE, PHILADELPHIA. 227 



The species is a characteristic Miocene fossil, as far as we now know. 

 It is rather stout, its nucleus is devoid of a calcarella ; the earliest whorls 

 show only a trace of transverse ribbing, while the spiral striation is quite 

 persistent. There are always three strong plaits beside that on the edge of 

 the pillar. The specimens I have seen are remarkably uniform in char- 

 acters. 



Subgenus Aurinia Adams. 

 Scaphella (Aurinia) mutabilis Conrad. 



Fine specimens of this species were obtained from the newer Miocene 

 by Mr. VVillcox from Duplin Co., North Carolina ; and specimens so close to 

 .S. diibia as to be doubtfully distinguishable, from the older Miocene beds of 

 St. Mary's River, Maryland. 



I have become convinced that the shell figured by Tuomey and Holmes 

 (PI. Fos. S. Car., pi. 27, fig. 6) as a variety of tmitabilis is really the adult 

 form o{ Aurinia obtusa Emmons ; at all events, we now have obtiisa of various 

 ages from the Miocene of Yorktown, Virginia, and Wilmington, Cape Fear 

 River, North Carolina; from the Pliocene of the Waccamaw beds of South 

 Carolina, and of Volusia Co., Florida. Whether mutabilis and obtusa must 

 not be referred as varieties to the type-form dubia (which was earliest 

 named) is a question which I do not feel able to answer. There is no doubt 

 that in the specimens we have examined there are, on the one hand, the 

 slender, straight, glossy dubia with a moderately small bulbous tip as figured 

 (pl- 7^ fig- 4) and with the canal not recurved. This grows to a large size 

 and has sometimes a larger, sometimes a smaller, tip to the shell — as every- 

 body who has opened the ovicapsules of such mollusks knows that, before 

 they make their way out, the larval shells are already of markedly different 

 sizes in the same capsule. On the other hand, we have the broad-tipped 

 obtusa, with a broader body-whorl in proportion than the others and a dis- 

 tinctly (though slightly) recurved canal. One could get along very well with 

 these if it were not for the obtrusive mutabilis, which in the same beds offers 

 every degree of mutation between the two extremes both in regard to the 

 curvature of canal and robustness of general habit, including the nuclear 

 whorls. The number of plaits in all is normally two, but Mr. Willcox 

 obtained a fragment of a very fine dubia at Magnolia, Duplin Co., N. C, 

 which has three plaits and may form a variety triplicata. The young of the 

 recent dubia shows two plaits, of Gouldiatta three plaits, and A. robusia 

 leads the list with four, which, however, in the adult are obsolete. 



Scaphella (Aurinia) virginiana Conrad. 



S. virginiana Conrad, part i. p. 80. 

 Volutifnsus typus Conrad. 



Older Miocene of Plum Point and the Patuxent River, Maryland, Harris 

 and Willcox; newer Miocene of North Carolina, Conrad. 



