1905.] NATURAL SCIENCES OF PHILADELPHIA. 225 



The jaw and teeth of Ashmunella do not differ from those organs in 

 Sonorella. The jaw is ribbed, the ribs variable and irregular, as is often 

 the case in the Californian Helices. It is less strong and the ribs are 

 less convex than usual in the jaw of Polygyra. The radula has from 

 24.1.24 to about 30.1.30 teeth. There are 9 to 12 lateral teeth. In 

 nine of the ten species examined, both mesocone and ectocone are bifid 

 on part of the marginal teeth. In A. duplicidens and A. chiricahuana 

 the ectocone is usually simple, but on occasional outer marginals of 

 the latter they are bifid, as in the other species. The number of teeth 

 reckoned as laterals varies somewhat on different parts of the same 

 radula, as I have observed in several species; so that the importance 

 of variations from the counts of teeth given in the text must not be 

 overestimated. Except in the case of A. chiricahuana, all of my prepa- 

 rations of genitalia, jaws and radulse are from specimens of the type 

 lots. 



From the data now in hand, it seems in a high degree likely that the 

 ancestral stock of all known Ashmunellas had a tridentate aperture. 

 There was a tendency to split the basal tooth, perhaps not expressed 

 in the original stock, but subsequently developed orthogenetically in 

 most of the subgroups. This tendency culminates in the levettei group, 

 where the original basal tooth has been divided into two distinct and 

 often widely separated teeth. There has also been degeneration of the 

 aperture-teeth, parallel in various stocks, and culminating in several 

 toothless forms, astonishingly alike, though of undoubtedly diverse 

 parentage. A. hyporhyssa Ckll., robusta Pils., chiricahuana Dall, esuri- 

 tor Pils., etc., are convergent forms of this character. The true rela- 

 tionships of such simplified species must be demonstrated by their 

 internal anatomy. The idea that the toothless forms are primitive can 

 hardly be entertained in view of their anatomical diversity and their 

 demonstrable relation to several groups of toothed species, the evi- 

 dently homologous teeth of wnich, on this hypothesis, would have 

 been independently evolved. This would be homoplasy on too 

 extensive a scale to be readily believed. 



The aperture-teeth in Ashmunella curiously imitate those of Polygyra, 

 a genus not in the least related. In Europe, Isognomostoma and Heli- 

 codonta have evolved similar forms in still other phyla. 



There has been a tendency to overload Ashmunella with subspecific 

 names, which would logically end in naming every colony in existence. 

 I do not minimize the importance of noting and recording local diiTeren- 

 tiation. My appreciation of its omnipresence convinces me that it 

 cannot all be stereotyped in nomenclature, and if it were, the result 

 would be too unwieldy for any human intellect to make use of. 

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