DENTALIUM. 25 



Bay of Panama, 26 and 30 fms., very abundant ; Galapagos Is., 

 in 812 fms.; off Guaymas, 20 fms. (U. S. F. Commission) ; Gulf of 

 Nicoya (Oersted) ; also Guaymas (Dall), apparently on the shore. 



D. oerstedii MORCH, Malak. Blatter, vii, p. 177 (1861). 



The hexagonal six-ribbed apex, with interstitial secondary and 

 tertiary riblets successively appearing in the intervals, are the more 

 obvious features of this form. The specimens from Panama Bay 

 and Galapagos Islands are lusterless and somewhat chalky. This 

 southern race is evidently the typical D. oerstedi which was de- 

 scribed from a rather short specimen. A translation of Morch's 

 diagnosis is as follows : 



D. oerstedii Mo'rch. Shell arcuate, rather solid, somewhat shin- 

 ing, white or yellowish, hexagonal at apex. Aperture circular, 

 having 12 lirse, the interstices smooth posteriorly, but toward the 

 middle divided by a riblet, whence to the aperture there are 24 

 lirse. Growth lines here and there more raised, nearly variciform. 

 Length 27, diam. 3 mill. 



Gulf of Nicoya, west coast of Costa Eica (Dr. A. S. Oersted). 



A specimen in the U. S. National Museum (no. 18,711) from Rio 

 Janeiro (U. S. Expl. Exped.) considerably resembles this species. 



Var. NUMEROSUM Dall, n. var. PI. 10, figs. 70, 71, 72, 73. 



This name, which Dall used to cover the entire species, as found 

 from Lower California to the Galapagos, may be utilized in a re- 

 stricted sense for the northern form. 



The general proportions and curvature are as in typical D. oer- 

 stedi, but the sculpture is less coarse ; tertiary riblets soon appear 

 on the concave as well as the other sides of tube, and toward the 

 middle a varying number of threads of a fourth order are inter- 

 posed ; toward the aperture all sculpture becomes flattened, and 

 the total number of riblets and threads is decidedly greater than in 

 typical oerstedi. The primitive 6 riblets retain their predominance 

 longer than in the type. The specimens are glossy. Length 41'5, 

 diam. of aperture 3'5, of apex 0'6 mill. 



Types of var. numerosum are no. 87,559, U. S, Nat. Mus. 



Off Lower California, near Cerros Id., lat. 28 12', long. 115 9 f 

 in 44 fms., and 24 1#, 110 ', in 26 fms. ; off Todos Santos, lat. 

 23 33', long. 110 37', in 66 fms. (U. S. Fish Commission). 



