DENTALIUM. 27 



D. pretiosum var. indianorum is far less coarsely sculptured than 

 this species, and the ribs do not crenulate the peristome. D. occi- 

 dentale is very similar, but the sculpture developed between the 

 primary ribs is unlike this Pacific form. D. majorinum and its 

 variety magellanicum are also much like agassizi, but the latter has 

 finer sculpture. The inner layer of shell substance is very dense 

 and bluish-white, the outer layer being softer and more chalky, fre- 

 quently eroded, often exposing the inside stratum which resists the 

 solvent power, at the apex and elsewhere. 



The number of riblets is quite variable ; thus the four specimens 

 measured above have : 



(a) At apex 20, at aperture 48 riblets. 

 (6) At apex 17, at aperture 40 riblets. 



(c) At apex 14, at aperture 29 riblets. 



(d) At apex 12, at aperture 25 riblets. (Off San Diego). 



The number of interposed riblets varies somewhat, but the num- 

 ber of apparently primary ribs at the apex is also subject to a wider 

 range of variation than usual. 



D. MAJORINUM Mabille & Rochebrune. PI. 12, figs. 98, 99. 



Shell moderately curved posteriorly, the later two-thirds nearly 

 straight, slender, attenuated toward the apex ; white, the young and 

 newer growth of adults somewhat translucent ; slightly shining. 

 Sculpture of about 11 narrow, rather acute ribs near the apex, separ- 

 ated by concave intervals ; the number increasing by intercalation 

 to about 29 at the aperture, where they are approximately equal, 

 with concave, transversely finely striate interstices, in some of which 

 a median riblet occurs. Aperture circular, not oblique. Anal 

 orifice minute and circular, without slit or notch. Length 38-5,^ 

 diam. of aperture 3'5, of apex 0"7 mill. 



West coast of Patar/07iia, 122 fnis. (U. S. F. C.sta. 2783) ; Orange 

 Bay, Patagonia (M. & R.). 



D. majorinum Mab. & RocH., Miss. Sci. Cap Horn, vi, Zool., 

 Moll., p. 100, pi. 4, fig. 10 (1889). 



Something is wrong with Mabille and Rochebrune's measurements 

 (their figure measuring, length 50, diam. at aperture 4'3 mill.), and 

 their description is not very good. It is here translated. 



Shell long-conic, rather slowly increasing, much attenuated to- 

 ward the apex, hardly shining, subpellucid, a little fragile, orna- 

 mented with numerous, nearly equidistant, somewhat roughened 



