14 MEMOIRS NATIONAL ACADEMY OF SCIENCES. [vol.xii. 



12. Angitremoides C. C. Adams. 1914. New. This anomalous form is found in the lower 

 part of the French Broad River at Dandridge, Tenn., and in the upper part of the Tennessee 

 River. The type is shown on plate 1, figure 12, Looneys Island, near Knoxville, Tenn., from 

 group 21, lot 124. The shells are as a rule spinose throughout life, judging from the apices. 

 These shells have the general appearance of young shells of the smaller specimens of turrita, 

 such as those of group 22, from the Lyon Shoals, below KnoxviUe, but instead of being thin, as 

 is the rule for young shells, these are thick, and the spines are relatively short, recalling those 

 of unakensis. 



This form has been found only in rather small numbers, and were it not for the mature 

 appearance of the shells, their short spines, combined with their relative small size, and their 

 occurrence in a large stream where large mature shells are to be expected, this form would 

 hardly justify recognition. 



In addition to the type specimen, others are figured as follows: From lot 136, plate 5, figures 

 28-30; Looneys Island, below Knoxville, lot 124, plate 5, figures 44-48 and lot 136 on plate 49, 

 figures 26, 28, 29, 31, and 32, and lot 137, figures 27 and 30. Possibly some individuals grade 

 into turrita, as in lot 152, from Loudon, Tenn. 



Two individuals of angitremoides, from lot 124, below Knoxville on Looneys Shoal, are shown 

 on plate 5, figures 45 and 47, which appear to have been smooth when at the class 2 stage. As 

 a rule this shell appears to be spinose at the class 1 stage. This lot is composed solely of one 

 kind of shell, of which there are 34 specimens in addition to those figured. 



There is a remarkable superficial similarity between this form and mature specimens of 

 Angitrema armigera Say, and hence the name of this form. Angitrema is a genus aUied to lo. 



13. Loudonensis C. C. Adams. 1914. New. This is a large spinose kind of shell whose 

 yoiing are without spines, corrugations, or nodules, but as the mature whorls are developed 

 the longest spines found in the genus are formed. Group 24, lot 152, from Loudon, Tenn., 

 and group 26, from between Dayton and Chattanooga, Tenn., exemplify this form. These 

 shells have been foimd most abundantly at Loudon, Tenn., and on account of the large homoge- 

 neous series which forms group 24, the type specimen has been selected from the series. 

 This is shown on plate 52, figure 12. The individuals of group 26 are more extreme in the 

 development of their spinosity, plate 54. In this form the young shell reaches considerable 

 size before the spines develop, as is clearly shown on the apical whorls on plate 52, and plate 

 5, figures 49-53. 



As shown by group 24, the width of shell is modal at 17.5 mm., plate 9. The globosity of 

 the shell is modal at 73 per cent, plate 13. The length of spines is modal at 3.3 mm., plate 17, 

 and the space between the spines reaches its maximum at 12.5 and 13.5 mm., plate 21. Group 

 26 has a maximum for distance between spines at 15.5 to 16.5 mm. 



The average height of spines, in groups 24 and 26, is modal at 27 per cent of the average 

 distance between them, plate 25. 



Undoubtedly this form has been confused, in collections, with spinosa and turrita. 



14. Turrita Anthony. 1860. This is a very elongate form with numerous close-set spines 

 and is spinose (probably) throughout life. A typical form is shown from group 27, lot 187, on 

 plate 55, figure 13, from Belief onte, Ala. It is a dead shell from the site of an ancient Indian 

 camp. The mode for shell width is at 22.5 mm., plate 9. The degree of globosity was not 

 determined for these old shells. Spine height is modal at 2.8 mm., plate 17, and the distance 

 between the apices of the spines is modal at 11.5 mm., plate 21. The average height of spine 

 is 27 per cent of the average distance between the spines, plate 25. 



The narrowness of the space between the spines allows a greater number per whorl than if 

 the space was larger as in loudonensis. 



THE GEOGRAPHIC RELATIONS OF THE SHELLS EXAMINED. 



As the shells were collected a special effort was made to seciire an exact record of the loca- 

 tion, particularly with regard to such landmarks as might enable others to closely approximate 

 the location. Such records are an essential part of a study of this character because, at times, 



