126 BULLETIN OF THE 



ooze; and 2383, in tfte Gulf of Mexico, in 1181 fms., mud, between the delta 

 of the Mississippi and Cedar Keys, Florida. 



The Gulf specimens, as usual, show a thinner and more glistening epidermk 

 over a sharper and more delicate sculpture and a thinner shell. Gymnobela 

 engonia Verrill may belong in this vicinity, but it has much more the aspect 

 of a genuine Bela. 



Section GYMNOBELA Verrill. 

 Pleurotomella (Gymnobela) extensa Dall. 



Plate X. Fie. 2- 



Pleurotoma {Bela) Blaheana var. extensa Dall, Bull. M. C. Z., IX. p. 55, August, 1881. 

 Pleurotoma (Defrancia) streptophora Watson, Linn. Soc. Journ., XV. p. 4G4, Nov., 

 1881 ; Chall. Gastr., p. 366, pi. xix. figs. 8 a-b, 1885. 



Habitat. Yucatan Strait, off Cape San Antonio, in 640 fms. ; Gulf of Mex- 

 ico, Station 35, in lat. 23° 52' and W. Ion. 88° 58', in 804 fms., bottom tem- 

 perature 40°. 5 F. Challenger Expedition, North Atlantic, in over 1000 fms. 

 Station not noted. 



It will seem extraordinary to many concnologists, that in my preliminary 

 paper I separated this form and the one which follows only as varieties. The 

 extremes look very unlike, but I separate them for convenience, and not be- 

 cause I am at all certain that all these Gymnobela;, excepting G. engonia Verrill. 

 and G. lotto; Verrill, do not belong to one and the same species. The single 

 characters which, in general, are common to them all, may be all or only in 

 part exhibited, may be absent, or each single, character may be weak or in- 

 tensified in strength, and the combinations of a few sculptural elements in this 

 way may exhibit an incredible number of forms, which in total, until carefully 

 analyzed, will seem very different from each other. The absence of struggle 

 which characterizes life in the deeps as opposed to that of the shores, and which 

 is illustrated by the absence of the protective operculum in so many species, 

 does not limit the variations of external form as they are limited by econom- 

 ical and other reasons where the struggle is intense. In estimating the archi- 

 benthal fauna this must be steadily kept in view. 



Pleurotomella (Gymnobela) Blakeana Dall. 



Plate X. Fig. 1. 



Pleurotoma {Bela) Blakeana var. normalis Dall, Bull. M. C. Z., IX. p. 54, August, 



1881. 

 Gymnobela brevis Verrill, Trans. Conn. Acad., VI. p. 417, pi. xliv. fig. 8, 1885. 



Habitat. Yucatan Strait, 640 fms. Gulf of Mexico, at Station 43, in 339 

 fms., mud, off Tortugas, bottom temperature 40°.0 F. ; Station 136, near Santa 

 Cruz, in 508 fms., soft ooze, temperature 42°. 5. U. S. Fish Commission, off 



