No. 2.] SNAILS OF THE GENUS 10— ADAMS. 13 



shell. This form must also be considered somewhat transitional between the smooth and 

 spinose forms, and it does not belong to a community of mixed spinose or undulate shells, as 

 do some other transitional series. There is a long distance between spiaes, the mode is at 9.5 

 mm,, plate 19. This appears to be the most stable condition in the Clinch River. The average 

 height of spines is modal at 17 per cent of the average distance between them, plate 23. 



The young shells are imperfectly known. Few immature shells were found, and the apices 

 of old shells are generally eroded. Two immature individuals, lot 17, Kyle Ford, are shown 

 on plate 3, figures 43 and 44. These indicate that the young are relatively smooth or corru- 

 gated, and that spines develop at an early age. 



9. Spinosa Lea. 1837. I have i-estricted the use of this term to shells which are very 

 spinose throughout life, from near Morristown, Tenn., in the Holston River. A typical speci- 

 men, from group 18, lot 96, is shown on plate 46, figure 7. As this series is fairly homogeneous, 

 its dimensions will be used in describing this form. The diameter of the shells is small and 

 variable, with a mode at 14.5 mm., plate 8. The globosity of the shells is relatively low and 

 variable, with a maximum ranging from 67 to 71 per cent, plate 12. The height of the spines 

 reaches a maximum from 1.8 to 2.3 mm., plate 16, This indicates very spiny shells, a degree 

 closely corresponding to that of recta (group 14) from Kingsport, farther upstream. The 

 distance between the spines is relatively very long, variable, and with a mode at 9.5 mm., 

 plate 20. The average height of spines is modal at 22 per cent of the average distance between 

 them, plate 24. The young shells appear to be undulate or spinose, as is indicated by the 

 apices of the older shells. 



The type locality given by Lea was the "Holston River, Washington County, Va." This 

 locality, for the kind of shell figured by Tryon (1873, p. 7) must be erroneous, because in this 

 county, on the South Fork of the Holston, I found only shells of the general type of group 13, 

 verrucosa, and in the North Fork the shells are of the similar nodular type. The Rotherwood 

 shells, group 11, recta, are the spinose shells which are the nearest geographically to the locality 

 given by Lea. Evidently the specimen of Lea must have come from farther downstream. 



10. Unalcensis C. C. Adams. 1914. New, This form is spinose throughout life, and is 

 confined solely to the headwaters of the Nolichucky River, group 19, lot 118, from Conkling, 

 Tenn. The type is shown in plate 47, figure 4. Only dead shells are known and these were 

 found about the site of old Indian camps. On account of the injured apertures, globosity could 

 not be determined accurately, and therefore only the diameter of the shell was measured. The 

 shell was found to be very variable and relatively narrow, the mode at 15.5 mm. and a secon- 

 dary maximum at 18.5 mm., plate 9. This is a degree of narrowness quite comparable to that 

 found in the headwaters of the Powell River. The spines are relatively low, with the mode 

 at 1,8 mm,, plate 17, also recalling the degree of spinosity found in the upper Powell. The space 

 between the spines is variable and has a maximum ranging from 7.5 to 9.5 mm., plate 21. The 



'average height of spines has its maximum from 17 to 22 per cent of the average distance between 

 them, plate 25. The young shells are spinose. 



11. NolicTiuckyensis C. C. Adams. 1914. New. This is the characteristic form of shell 

 in the lower part of the Nolichucky River. The shells are spinose throughout life, as shown 

 by the young and by the apical whorls. The small spines on young shells are sharp pointed 

 and not corrugated or nodulate, as are the relatively spinose shells in the headwaters of the 

 Powell, Clinch, and Holston Rivers. This form is represented by group 20, lot 104, from White 

 Pine, Tenn, The type is figured on plate 48, figure 13, The shell is very narrow and very 

 variable, with a mode at 11.5 mm,, plate 9. In general terms, these are the narrowest shells 

 of the genus. The degree of globosity of the shell is modal at 73 per cent, plate 13. Spine 

 height is modal at 1.8 mm., plate 17. The space between the spines is variable, with a maxi- 

 mum at 7.5 and 8.5 mm., plate 21, which is a relatively narrow space between the spines. This 

 narrowness is probably influenced, as are also the other dimensions, by the large number of 

 young shells present in the group, plate 48. The average height of spines has its maximum at 

 22 per cent of the average distance between them, plate 25. 



