38 



BULLETIN 111, UNITED STATES NATIONAL MUSEUM. 



DENTALIUM (ANTALIS) AGILE SUBAGILE, new subspecies. 



Plate 4, fig. 8. 



1879. Dentalium entails orthrum W atso'^ , Journ. Linn. Soc. ZooL, vol. 14, p. 612, 



in part. 

 1886. Dentalium entalis orthrum Watson, Challenger Report Seaphopoda, p. Ck 



in part. 

 1897. Dentalium entalis orthrum, Pilsbry and Sharp, Tryon's Man. Conch., vol. 



17, p. 44, in part. 

 1897. Dentalium (Antalis) agile, Pilsbry and Sharp, Tryon's Man. Conch., vol. 



17, p. 46, in part (not pi. 8, fig. 36); (not D. agile, Ball, Bull. Mus. Comp. 

 Zool., vol. 9, p. 37, 1881); (notZ>. agile, Dall, Bull. Mus. Comp. Zool., vol. 



18, p. 418, 1889). 



1901. Dentalium agile, Whiteaves, Cat. Marine Inv. of E. Canada, p. 152. 



1908. Dentalium agile, Lermond, Shells of Maine, p. 15. 



1915. Dentalium agile, Johnson, Occ. Papers, Boston Soc. Nat. Hist., No. 7, p. 83. 



The shell is very long and slender; slowly and regularly increasing 

 in diameter from tip to oral end; it is of moderate degree of curvature, 

 pronounced in the tip. The degree of curvature is, however, a variable 

 feature in this species, some specimens bemg nearly straight. It is of a 

 dull ashy -white color and possesses a thin outer layer of varying 

 degrees of hardness, covermg a middle chalky -white layer, which 

 in turn surrounds an inner hard but thin nacreous layer. The outer 

 surface usually flakes off m spots and exposes the chalky texture 

 underneath to the destructive action of the sea water. The sculpture 

 consists of about 18 longitudinal, narrow riblets, separated by wider, 

 rather smooth, shallow spaces between them. The riblets are not 

 increased by mtercalation, and continue, though gradually fadmg, 

 to the aperture except m very old specimens. Between some of the 

 primary ribs there may be occasionally detected some very fine 

 longitudmal lines, which are, however, of minor importance, as they 

 rarely persist. Coarse, irregular growth Imes are more or less apparent 



