EAST AMERICAN SCAPHOPOD MOLLUSKS. 31 



The type, Cat. No. 161568, U.S.N.M., measures: Length, 42 mm.; 

 diameter, 3 mm.; arc, 4 (without tip). It is from Mayaguez Harbor, 

 Porto Kico, U. S. B. F. Station 6062, in 25 to 30 fathoms, on bottom 

 of sand mud and shells, bottom temperature 75.8° F. Another lot of 

 two young specimens, Cat. No. 161567, U.S.N.M., is from the same 

 station. 



DENTALIUM (DENTALIUM) GOULDII COLONENSE, new subspecies. 



Plate 3, fig. 6. 



1889. Dentalium gouldii Dall, Bull. Mus. Comp. Zool., vol. 18, p. 424, in part. 

 1897. Dentalium gouldii, Pilsbry and Sharp, Tryon's Man. Conch., vol. 17, p. 20, 

 in part. 



The shell is highly polished, glassy, thin but strong, milky white, 

 and of fairly even curvature. Tlie apical fifth is hexagonal with ribs 

 very narrow and rod-like, giving wide intercostal spaces which show 

 evanescent microscopic longitudinal engraved lines, less distinct 

 than in D. g. gouldii but more so than in D. g. portoricensis . In the 

 second fifth from the apex intercalation of one secondary rib between 

 each two primaries begins and later additions confuse the hexagonal 

 section of the shell. All ribs tend to decrease, and the anterior third 

 of the shell is round, smooth, and vitreous, no trace of any sculpture 

 remaining. No notch or slit is showm in the National Museum 

 specimen. 



The type, Cat. No. 94085, U.S.N.M., measures: Length 35 mm.; 

 diameter. 2.75 mm.; arc, 2; was dredged at the U. S. B. F. Station 

 2145, near Colon, in 25 fathoms, on green mud and broken shells, no 

 bottom temperature record being given. The type is the unique 

 specimen. 



This shell differs from the typical subspecies in the lesser develop- 

 ment of all the sculptural characters, and again in the intercalation 

 of secondary ribs, and finally in its degree of curvature. 



DENTALIUM (DENTALIUM) REBECCAENSE, new species. 



Plate 3, fig. 2. 



Tavo lots in the National Museum collection belonging to the group 

 of hexagonal tip species resist identification with any of the published 

 forms. The specimens are all juvenile, but I am sufficiently convinced 

 they are new to venture upon a description, even though the adult 

 cliaracters can not be given. 



The shell is hexagonal, with a very attenuate and sharply curved 

 tip, the six angles quickly assuming the character of pinched-up 

 rounded ribs, separating rather broad, not quite flat intercostal 

 spaces. No fine sculpture is indicated, but lines of opacity in a 

 portion of the spaces between the ribs sometimes simulate a very 

 close transverse system of lirae. There is no intercalation of sec 

 ondary ribs in these thin, white juvenile specimens, nor notch nor 

 other apical characters observable. 



