No. 2.] 



SNAILS OF THE GENUS 10— ADMIS. 



63 



in the lower French Broad, Lower Holston, Tennessee, and allied variations of similar develop- 

 ment are found extending up the Powell to group 2, and up the Clinch to group 7, thus far into 

 the headwaters. 



Table showing the ontogeny of shell sculpture in lo. 



Name. 



Embryonic whorls. 



Class 1. 



Class 2. 



Class 3. 



Class 4. 



Class 5. 



1. powellensis . 



2. clinchensis . 



3. fiuvialis 



4. lyttonensis. 



5. paulensis... 



PI. 3, figs. 1, 2. 



Unlaiowii, probably 



smooth. 

 ....do 



....do 



Probably smooth. 



6. loudonensis.. 



UrLknown, proba- 

 bly smooth. 



7. verrucosa. 



.do. 



8. brevis. 



.do. 



9. recta 



10. unakensis 



11. nolichuclcyensis.. 



12. spinosa 



13. angiiremoides 



.do. 



.do. 



14. turrita 



Chissolms Ford, lots 



97, 98. 

 Pemiington Gap, 



lot 39. 



PI. 5, figs. 16-25, 

 smooth. 



PI. 5, fig. 12, smooth. 



Umknowii, probably 

 smooth. 



do 



PI. 3, figs. 60, 61, 65, 

 smooth. 



PI. 29, figs. 32, 37, 39, 

 unknown, proba- 

 bly smooth. 



Smooth. 



Unknown, proba- 

 bly smooth. 



Smooth or undu- 

 late. 



Smooth 



do 



PI. 52, smooth. 



PI. 4, fig. 7, smooth 

 (?) or corru- 



Pl. 3, figs. 43, 44, 

 smooth or corru- 



Pl. 42, spmose 



PI. 47, figs. 14-16, 



spmose. 

 PI. 48, spmose 



Spmose 



Unknown, proba- 

 bly spinose. 

 Probably spinose . 

 do 



Probably smooth. . 



Smooth. 



.do. 



Smooth or corru- 

 gated. 



Keel smooth 



Smooth or undu- 

 late. 



Smooth. 



Corrugated. 



Smooth or corru- 



Smooth (?) or 



spmose. 

 do 



.do. 



Spinose 



Rarely smooth, 

 spinous. 



Spmose 



do 



Smooth. 



Smooth. 



.do. 



Smooth or corru- 

 gated. 



Small spines 



Smooth or undu- 

 late, rarely spi- 

 nose. 



Smooth, or nodu- 

 lose on younger 

 part. 



Corrugated or nod- 

 ulose. 



Spinose. 



do... 



do... 



....do... 



..do. 

 ..do. 



.do. 

 .do. 



.do. 



Smooth, or shoul- 

 der, keel, nod- 

 ules, late in this 



Smooth, or shoulder, keel, nodules, late 



in this stage. 

 Smooth or corru- 



Small spines. 

 Spinose 



Large, spinose. , 

 Nodulose 



Spinose, some 

 spines ' 



Very spinose. 



Spinose. 

 Do. 



Spinose, some 

 spines keeled. 



Spmose 



do 



do... 



Smooth . 



.do. 



Sp nose. 

 Do. 



Do. 



[Inverse develop- 

 ment. 



Discussions and general summary. — The smoothest young shells are found in the head- 

 waters of the Powell, group 1, and as a rule they do not become carinate or spinose. These are 

 the form powellensis. Some individuals, however, as they approach maturity, or are mature, 

 do develop a carina, nodules, or spines, and they thus grade into the form lyttonensis which is 

 represented by a few individuals even in the headwaters. Lyttonensis develops spines at the 

 class 3 stage, so that one can not tell into which kind of an adult a very young smooth shell wiQ 

 develop, because both kinds of young are intermingled in this region. This is in a population 

 of shells which is primarily smooth. 



The shells of group 2 are smooth, or until they reach the class 3 stage, when a sculpture 

 may be developed and continue, or this sculpture may be lost, and thus show inversion. The 

 shell population is mainly spinose and of the form lyttonensis, but mingled with them are forms 

 which intergrade, in sculpture, into the smooth form powellensis. Thus there is a condition 

 which is the reverse of that found in group 1 . Inversion is relatively abundant in these shells 

 and the sculpture develops earlier than in powellensis. 



In the lower Powell, the young shells at the class 1 and 2 stages, and the apices of older 

 shells, may be smooth or spinose, and the adults show similar differences. Kelatively 

 smooth shells are few in number, and they often show indications of spines, which suggest 

 contamination by the spinose shells. The population is not homogeneous, but is much mixed. 

 Spinosity develops much earlier than in the headwaters, and inverse development is generally 

 of relatively rare occurrence in the Powell. 



In the Clinch immature shells were not found in group 6, but it is highly probable that the 

 young are smooth or undulated. Nodules develop irregularly on adult shells with approaching 

 maturity. In group 7, at the class 2 stage, the shell may be smooth or develop corrugations, 

 and these corrugations may or may not develop later into spines. Nodules or spines rarely 

 develop on a shell in the class 3 stage, but are found abundantly upon mature shells, and many 

 mature shells remain without spines. In group 8 the transition has been made from the pre- 

 dominance of smooth to the spinose shells. The shells tend to become spinose before maturity 



17829"— 15— 5 



