90 Bulletin ii 90 



tion, among those which had been referred to as N. aperta Whit- 

 field, has an incipient callus forming, and I am led to suspe(5t 

 that this species delays forming a callus until the shell is fulh^ 

 grown and then adds it, and that therefore N. aperta and A^. 

 onusta should be consolidated under the last mentioned specific 

 name." Opposed to this view are the fadls: that even the small 

 onicsta are provided with a callus; that their shell substance is 

 thicker than in aperta; that there is scarcely ever a trace of a 

 shoulder just below the suture in onusta^ while it is strongl}' de- 

 veloped in aperta; aperta' s spire is generally much more elevated 

 and pointed. 



This we believe to be a forerunner of N. limula. The latter 

 species was recorded in Bull. 4 as coming from the Midway beds. 

 Having up to this time seen no other specimens from so low a 

 horizon, or even from the Lignitic, we are inclined to suspe(5l an 

 error in labelling sorfiewhere. A^. onusta varies somewhat in form, 

 but no more than does limula. It is distinguished from the latter 

 by its umbilical features only. Its umbilicus is very broadly 

 spreading, hence giving the lower margin of the body whorl a 

 more or less carinated appearance. The greater part of this um- 

 bilicus is filled by a callosity that has no transverse bisedling de- 

 pressed line across it, as limula does. It is typicall}^ developed 

 at Yellow bluff. 



Localities. — Ala.: Yellow bluff; Gregg's landing; Bell's land- 

 ing; Woods bluff; Nanafalia? Aldrich adds Tuscahoma. 



Specimens figured. — lyarge depressed form, Yellow bluff; very 

 elevated form, Gregg's landing; smaller specimen. Bell's landing. 

 All in Paleontological Museum, Cornell University. 



Natica aperta, PI. 11, fig. 27. 



Syn. Natica {Girodes) aperta Whitf., Am. Jr. Conch., vol. i, p. 265, 

 1865. 

 A", aperta Aid., Geol. Surv. Ala., 1886, Bull, i, p. 56. 

 N. {Neverita) aperta Dall., Trans. Wag., etc., vol. 3, p. 368. 



Whitfield' s original description. — "Shell very oblique, palulose; 

 spire low; volutions three, slightly flattened on the top, with a 

 depression just below, and sharply rounded on the lower part; 

 umbilicus very large; upper part of the columellar lip refledled 

 over the umbilicus; callus, none; aperture large, semi-lunate; 



