32 BULLETIN 111, UNITED STATES NATIONAL MUSEUM. 



The type, Cat. No. 314293, U.S.N.M., measures: Length, 13 mm.; 

 diameter, 1.75 mm.; arc, 1. It was dredged between Tortugas and 

 Rebecca Shoals, Florida, in 16 fathoms on coral sand, Eolis Station 33, 

 and is chosen from a lot of 26 specimens. 



Another specimen. Cat. No. 314294, U.S.N.M., comes from 5 miles 

 off the north entrance to Key West Channel in the Gulf of Mexico, 

 7 fathoms, sand bottom, being Eolis Station 30. 



The hexagonal section is confined only to the tip, as the angles 

 quickly assume the character of primary ribs, as in D, laqueatum, thus 

 differing from D. texasianum and D. gouldii, nor are the intercostal 

 spaces as broad or as flat as in those last two species. Tiie exceed- 

 ingly slender curved tips are like delicate spun glass, transparent and 

 fragile; the intercostal spaces remain very thin and break at the 

 aperture rim, leaving the peristome with the ribs projecting as in 

 young D. laqueatum. 



Superficially the little shells look exceedingly like the tips of D. 

 laqueatum, but tliey are at once distinguishable by their more slender 

 shape and again by the total absence of a reticulated surface. 



DENTALIUM (DENTALIUM) OBSCURUM Dall. 



Plate 3, figs. 1, 3. 



1889. Dentalium gouldii obscurum Dall, Bull. Miis. Comp. Zool., vol. 18, p. 424, 



pi. 27, fig. 41. 

 1897. Dentalium gouldii obscurum, Pilsbry and Sharp, Tryon's Man. Conch., vol. 



17, p. 20, pi. 7, fig. 4. 



The shell is awl-shaped, or in general, straight with a moderate 

 curve only in the tip, and is regularly though slowly increasing in 

 diameter. It is vitreous, solid, thin but strong, and with an oily 

 white surface. The tip is polygonal, with nine primary ribs, narrow 

 and sharp, separating flat wide spaces. At the beginning of the 

 second third from the apex the ribs increase by intercalation to twice 

 the original number or even more. All the ribs, both primary and 

 secondary, assume about equal importance and take on a roughened 

 wavy aspect, as though irregularly noduled, an effect seemingly, 

 though not really, caused by growth lines; these growth lines may 

 be seen as merely microscopically fine transverse scratches. The 

 surface character continues to the oral end of the adult shell, there 

 being no degeneration of the ribs into a smooth cylinder. No apical 

 notch or slit is indicated. 



The type and four specimens, Cat. No. 95351, U.S.N.M., were 

 dredged by the BlaJce, U. S. C. S. Station 229 off Barbados, in 140 

 fathoms, on a bottom of coral and broken shell, and temperature of 

 56.5° F. 



One specimen, Cat. No. 95372, U.S.N.M., also taken by the BlaJce 

 at U. S. C. S. Station No. 300, off Barbados, in 82 fathoms, bottom 

 temperature 60°. 



