80 TRANSACTIONS OF THE WAGNER FREE 



prominent than in M. lincolata this portion of the shell appearing nearly 

 smooth and towards the base, best seen on the back, they are no longer 

 elevated but impressed, or impressed with a marginal carination, a feature 

 not seen in M. lineolata, in which all the lines are elevated ; in M. Caro- 

 linensis the infra-sutural excavation, besides being narrower, is clearly 

 defined on several of the whorls, whereas in M. lineolata it is apparent as 

 such only on the body-whorl ; the whorls of the spire in M. Caroline nsis 

 are much more distinctly convex, whereas the elevated ridges are not 

 nearly as sharply defined as they are in M. lineolata. The young of M. 

 lineolata is equally ridged over the entire surface, which does not appear 

 to be the case with M. Carolinensis. 



Despite the differences here indicated, there can hardly be a doubt, it 

 appears to me, that the two forms are merely derivatives one from the 

 other an expression of the ceaseless law of evolution.* 







Harginella limatula, Conrad. 



Jour. Acad. Nat. Sciences, Phila., vii, p. 140. 



I identify a shell from the Caloosahatchie with this species, which 

 may, perhaps, be properly considered to be only a variety of the recent 

 M. apicina of Mencke. The typical forms of the latter, however, differ 

 in the produced spire and in lacking the prominent denticulations on the 

 labrum. In the series of Marginellas obtained by Gabb from the 

 Miocene deposits of Santo Domingo, and identified by that paleontolo- 

 gist with M. apicina, we have the gradual passage leading from the high- 

 spired form to the form in which the apex is almost completely buried 

 in the callus developed by the rising outer lip ; the character of the 

 crenulations on the labrum is also shown to vary considerably. Gabb's 

 form appears to be identical with the species from the Caloosahatchie, 

 and, as far as I can determine, is undistinguishable from the Miocene 



fossil of the Carolinas and Virginia. The species referred to by Tuomey 







* Since writing the above I have obtained for comparison, through the kindness of Prof. 

 Whitfield, of the American Museum of Natural History of New York, the specimen which 

 Tuomey and Holmes identified with Conrad's species. This shows a character of ornamen- 

 tation more nearly that of the Florida fossil, but the convexity of the spiral whorls, and the 

 lesser prominence of the revolving ribs or sulcations, serve readily to distinguish it from 

 that species. It really stands intermediate between the typical Mitra Carolinensis and 

 Mitra lineolata, although nearer the former, and whether all three should now be united 

 into a single species, or the extremes, which are very well marked, be retained apart, is a 

 matter of little import. It is manifest that with the continued discovery of intermediate 

 forms the classification of species (and no less that of genera, etc.) will become UK ire :ind 

 more artificial and arbitrary, necessitating ultimately, if convenience is still to be con- 

 sidered, the placing of the same "specific " form, with its attendant varieties, into a series 

 which might include distinct species, genera, families, or even orders. For it cannot be 

 denied that the relationship established through phylogeny is at least as important from a 

 classificatory point of view as that furnished by the taxonomic characters derived from 

 living forms alone. 



