MUSEUM OF COMPARATIVE ZOOLOGY. 123 



Pleurotomella chariessa Watson, typical. From this Verrill's PL Jeffreysii 

 cannot be separated. 



PI. chariessa var. spica Dall. Shell more slender and elongate, 58 X 18 mm., 

 with eleven whorls, not counting the lost nucleus ; 966 fms., Jamaica, W. I. 



PI. chariessa var. phalera Dall. Slender like the last ; the transverse riblets 

 fewer, longer, and stronger, the plaits in front of the suture on the anal fasciole 

 fewer or obsolete ; the canal shorter and wider; 38 X 14 mm.; nine whorls 

 and the nucleus. Off Cape Fear, N. C, in 731 fms., ooze. 



PI. chariessa var. tellea Dall. Shorter, much like the typical form, but the 

 transverse riblets and sutural plaiting strong only on the early whorls, absent 

 or obsolete on the last two or three ; the spiral lines absent or obsolete ; the 

 shell glossy ; 29 X 1 1 mm ; six and a half whorls and the nucleus ; with the 

 preceding. 



PI. chariessa var. aresta Dall. Shell shaped like variety phalera but with 

 the suture less excavated, and therefore looking more compact, the spiral sculp- 

 ture more deeply cut, and the transvere riblets more elongated forward, a little 

 more numerous and more distinctly defined ; the canal is also a little narrower; 

 28 X 10 mm. ; eight whorls and the nucleus; with the preceding. 



It is possible that a good many conchologists might regard the above vari- 

 ations as of specific value, but I cannot bring myself to believe that they are 

 equivalent to species or what we are accustomed to regard as species among 

 shallow-water forms, where variation is more limited by the intensity of the 

 struggle for existence. 



Pleurotomella filifera Dall. 



Plate XII. Fig. 9. 



Pleuroloma (Bela) Jilifera Dall, Bull. M. C. Z., IX. p. 56, August, 1881. 



Habitat. Station 47, in 331 fms., Gulf of Mexico. 



This species is chiefly separated from P. chariessa by its stronger spiral sculp- 

 ture and proportionally shorter canal. The nucleus also, though eroded, seems 

 to have been considerably smaller than that of chariessa when perfect. A 

 larger amount of material might perhaps connect the two, but I do not see 

 my way clear to unite them at present. 



There now follow a few species which are intermediate between Pleuroto- 

 mella, especially such forms as P. Bairdii Verrill, and those called Gymnobela 

 by Verrill. I am unable to see, either in the shells themselves or in the 

 diagnoses, any differences of generic value between Pleurotomella and Gymno- 

 bela, except that the small and short stout forms are placed by Professor Verrill 

 in the latter group. The animals have similar dentition, similar larval shells, 

 and are similarly destitute of operculum and generally of eyes. It does not 



