330 BULLETIN OF THE 



Niso interrupta Sowerbt. 



Plate XVIII. Figs. 6, 6. 



Nlso interrupla A. Adams, he. cit., pi. clxx. fig. 9. 

 Eiilima interrupta Shy., F. Z. S. 1834, fig. 9. 



Niso ceglees Bush, Trans. Conn. Acad. Sci., VI. p. 465, pL xlv. figs. 10, 10 a, 1885; 

 Annual Rep. U. S. Fish Commission for 1883, p. 83, 1885. 



Habitat. Gulf of Mexico at Station 36, in 84 fma. Barbados, 100 fms. 

 Station 220, near Santa Lucia, in 116 fms., rocky bottom, temperature 58°.5 F. 

 East coast of the United States, south of Hatteras, U. S. Fish Commission. 

 West coast of Central America, Cuming. Japan, Dunker. 



All the species of Niso, so far obtained from the east coast of the United 

 States and Central America, are probably derivable from one species. They 

 differ only by trifling distinctions of form and by their colors. The northern 

 specimens, whatever their color, have the whorls slightly flatter than those 

 from the Antilles or the Gulf. 



The variations are as follows: — 



White, with traces of color at the varical angles. (Sta. Lucia.) N. interrupta 

 var. albida, Dall, PL XVIII. figs. 5, 6. 



White, with brown keel. (Barbados.) Var. circinata Dall. 



Pale brown, with narrow dark brown keel, no white bands. (Gulf of Mexico 

 and West America.) N. interrupta s. s. 



Pale brown, with broad brown band between two white bands at periphery. 

 (Hatteras, N. C, 15-107 fms.) N. interrupta var. tricolor Dall. 



Brown, more or less suffused with purple, brown band narrow, no w^hite 

 bands, flushes of purple brown on base and behind varices. (Carolina coast, 

 7-100 fms.) N. interrupta var, ceglees Bush. 



Umbilical keel with white band on each side, other colors like var. tricolor ^ 

 but all the white bands articulated with chestnut spots. N. (var. ?) splen- 

 didula Sby. 



All of these forms exhibit transverse evenly distributed sharp straight 

 scratches, extending forward from the suture. In general, they are difficult to 

 see on account of the polish of the surface. The proportions are the same in 

 all, but the young are more sharply keeled at the periphery. The keel is 

 obsolete in the adult shell. The length and number of whorls of the largest 

 specimen of each variety I have been able to examine are as follows : — 



1. N. splendidula. Lon. 27.0, lat. 10.0 mm., whorls 17. 



2. N. interrupta var. tricolor. Lon. 18.5, lat. 8.0 mm., whorls 14. 



3. N. interrupta var, ceglees. Lon. 12.0, lat. 4.8 mm., whorls 12. 



4. N. interrupta var. albida. Lon. 8.1, lat. 3.5 mm., whorls 11. 



5. N. interrupta var. circinata. Lon. 6.6, lat. 3.0 mm., whorls 9. 



6. N. interrupta s. s. Lon. 14.3, lat. 5.6 mm., whorls 14. 



In the above list the nuclear whorls are not counted in any, since they are 

 lost from some of the examples. Only numbers 1 , 2, and 6 were sufficiently 



