1888.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 377 



P. simplex Gld. has also been arranged among Vertigo by a number 

 of prominent conchologists. No further proof is wanting to show that 

 its place is not here; it should be stated, however, that it is absolutely 

 identical with P. edentula Drap., inhabiting the Old World as well as 

 the New. By European conchologists it is regarded as the main recent 

 representative of the group or subgenus Edentulina. Draparnauci's 

 name will have to be substituted for Gould's. 



We will now consider two species deserving of special attention, both 

 European, viz, P. pusilla Miill., and P. venetzii Charp. (P. angustior 

 Jeffr.), which have been placed in a group of Vertigo under the sub- 

 generic name of Yertilla, both of them being sinistrorsal or reversed 

 forms. After a critical examination and comparison I came to the con- 

 clusion that oue of them, the latter, is nearly related to our North Ameri- 

 can P. milium Gld., while P. 2)usillais quite different. 



One thing which at first attracted my attention, the fact that each 

 of these has a very long lamella in the outer wall (fig 10), which is 

 readily seen through the transparent shell (figs. 12,13), but while in 

 P. venetzii the upper, E 5 is the largest, in P. milium it is the lower, D. 

 Now, a careful examination will reveal the fact to any observer that 

 in position each of these long folds is different from the other, but 

 that the folds themselves are alike in both species ; a morphological ele- 

 ment quite unique. It is a long, thin, high lamella, beginning rather 

 deep in the throat, and close to the base, in a direction with or near 

 the lines of growth, then turning upward and toward the aperture, 

 and meeting the lower primary lamella D in P. milium, and the upper 

 E in venetzii. This may appear as a rather bold assertion, yet, never- 

 theless, I believe it to be in conformity with nature, and moreover 

 it is not without analogy, as it is well known iu many Clausilias two 

 lamella 1 on the body whorl may be entirely separate, or again, other- 

 wise unite in apparently one, in which, however, a careful examination 

 will detect the two elements, and nearly the same is to be seen in some 

 Pupae. May not the lamella in question be regarded as the homologue 

 of the lunar, and partly gnlar fold of Clausilia, only more differentiated 

 in the latter? 



This feature alone is important enough to justify a separation of 

 these two species from Vertigo, and to warrant the creation of a sub- 

 genus for them, but not alone on the point named ; there are other 

 characters also. Before considering these, I will say a few more words 

 concerning the former. The gular lamella is generally larger in P. 

 venetzii where its inner end cau not be seen from the aperture (figs. 11, 

 12), than it is in P. milium ; I found it shorter and a little curved in 

 small specimens of the latter from Ced:ir Keys, Florida ; yet it is doubt- 

 less the same thing as in others from Illinois, where it exhibits almost 

 exactly the same size and curvature as in P. venetzii. As a proof of 

 the distinct nature of the gular fold, it should be mentioned that in 

 several examples of P. milium not fully mature, it has been found 



