24 BULLETIN 111, U:NriTED STATES NATIONAL MUSEUM. 



shell. The nepionic tip is preserved in a Barbadian specimen which 

 merits a description. The extreme end is bulbous, with a flaring 

 opening which is somewhat produced or drawn out, and is perfectly 

 smooth, exceedingly thin, and glassy. This bulbous portion of 

 about 0.2 mm. length is followed by a constricted neck of about 0.2 

 mm. length, around which are several prominent growth bands. 

 Following this constricted neck the shell begins its normal increase 

 in girth as an exceedingly fragile round tube 1 mm. long, upon which 

 appear faintly the beginnings of the primary ribs. These ribs in- 

 crease in definiteness until the shell loses its round section and be- 

 comes polygonal in form. These primaries show a minute serration 

 even before the interspaces assume their characteristic transverse 

 sculpture. All of the portion so described, which measures about 

 3 mm. in length, is broken off and lost except in very rare instances. 

 A normal tip measurement is: Length, 25 rmn., diameter, 4 mm., 

 with an arc of 3.1. 



Variations are slight and may be referred chiefly to the degree of 

 persistence shown by the primary ribs before they become flattened 

 and finally merged into the smoothish anterior portion. 



The type, Cat. No. 44671, U.S.N.M., was dredged at United States 

 Bureau of Fisheries Station 2268 off Cape Hatteras, in 68 fathoms, 

 gray mud, bottom temperature 71.3° F. 



The extensive series in the National Museum collection shows 

 extremes of depth from 10 to 193 fathoms and ranging from the 

 Hatteras region to Barbados, including the Gulf of Mexico. It 

 appears to be a very abundant species in the sandy mud (^ 'green 

 mud") along the inner edge of the Gulf Stream in the Florida Keys 

 region, especially from off Fowey Light and Cape Florida. 



It is an exceedingly well-marked species of very definite characters 

 and not easily to be confused with any other species of the western 

 Atlantic. Two subspecies are indicated. 



DENTALIUM (DENTALIUM) LAQUEATUM LAQUEATUM Verrill. 



Plate 1, figs. 6 and 7. 



This subspecies includes the forms presenting the sculptural 

 features described under D. laqueatum, (p. 23) as losing distinctness 

 and form in the anterior portion of the shell. All the sculptural 

 elements of this species, consisting of primary and secondary ribs 

 and a finely reticulated surface covering both the ribs and the spaces 

 between them, become gradually merged into a smooth though not a 

 polished surface. The type is the same as of D. laqueatum. 



The following lots are in the United States National Museum 

 collection: 



