THE NAUTILUS. 123 



It may be stated as proven that some colonies consist of " pento- 

 don " and intermediate forms; some of "pentodon," intermediate and 

 " curvidens " forms ; and some of the intermediate and " curvidens " 

 forms. We have found no large gathering of wholly typical pentodon 

 or entirely curvidens. Either form may be found with a low or high 

 crest — this being usually more constant in any one colony than the 

 number of teetli or the size and shape of the shell. The only theory 

 upon which curvidens could be retained as a species or subspecies 

 would be to assume that two species are living in a state of hybri- 

 dism — an assumption which seems to us baseless. 



Bifidaria pentodon gracilis Sterki. Figs. 16 to 27. 



This is usually larger, more cylindric, with 5 teeth, though per- 

 fectly mature shells may have as few as 3 (figs. 19, 26,) or as many 

 as 6 or 7 (figs. 16, 18, 21). It was originally described from New 

 Philadelphia, Ohio, but those figui'ed are from Alabama; figs. 16, 17, 

 21 to 27 from around Wetumpka, 18, 19, from Woodville, 20 from 

 Big Wills Valley, coll. by H. H. Smith and H. E. Sargent. None 

 of them has an infraparietal denticle. 



While this race seems to be tangibly differentiated in the hill 

 region of Alabama, specimens may be selected from other lots of 

 pentodon which could not possibly be distinguished if mixed with the 

 Ala. shells ; for instance fig. 31, Henry Co., Ind., and fig. 33, Des 

 Moines, la., both taken from lots varying in shape from long and 

 cylindric to shorter and more conic. 



The original descriptions of forms referred to pentodon here follow. 



" V. pentodon. Shell dextral, subovate, whitish horn-color ; apex 

 obtuse ; whorls five, glabrous, convex ; suture not very deeply im- 

 pressed ; aperture semioval ; labium two-toothed, of which a single 

 very prominent one is on the middle of the transverse portion or true 

 labium, and the other is remote, much smaller and placed in the 

 basal angle of the columella ; labrum regularly arcuated, tridentate, 

 tooth nearest the base very small and placed near the smaller tooth 

 of the columella, the two others larger, subecpial ; umbilicus distinct. 

 Length less than one-tenth of an inch. 



" Animal. Tentacula two, rather long and (hick, cylindrical-ob- 

 conic, retractile, with a rounded oculiferous extremity ; two hardly 

 elevated truncated tubercles instead of the anterior tentacula ; foot 

 white ; head and neck, as far as the mantle, black. 



