328 



PROCEEDINGS OF THE ACADEMY OF 



[May, 



At Station 5 two broken examples, 

 much weathered, were dug out of the 

 soil. Though practically adult, the 

 largest measures only 18.2 mm- diam- 

 eter, the shell being quite as solid as 

 in large individuals. It was probably 

 dwarfed by the arid conditions be- 

 fore it became extinct in this place. 



The genitalia are remarkable for 

 the small size of the male organs. 

 The penis is very slender, diameter 

 1 mm., tapering downward, and en- 

 circled at the base by a short sheath. 

 The penis-papilla is very slender, 

 gradually tapering, and annulate. The 

 retractor muscle is terminal, long and 

 slender. Epiphallus a little shortei' 

 than the penis. The vagina is slightly 

 longer than the penis. Other organs 

 as usual. Measurements of the organs 



of two individuals are given in the following table, with those of 



allied forms for comparison. 



Fig. 2. — Genitalia of S. hachi 

 tana, with detail of penis 

 papilla. 



S. hachitana 



S. h. flora 



It 

 S. h. pelonciUensis 



o 



S 



3 

 0) 



33 



103,098 

 103,098 

 94,329 

 94,329 

 86,496 

 94.513 

 94,513 



The well-arched jaw has 7 or 8 ribs. The radula has about 22, 16, 

 1, 16, 22 teeth, both cusps becoming split on the marginal teeth. 



In my former work on S. hachitana (1905) I referred shells from the 

 Organ and Florida Mountains and from central Arizona to S. hachi- 

 tana, which at that time was not known anatomicall3^ While it 

 must be admitted that the shells are very similar, I find differential 



