124 THE NAUTILUS. 



eight angled, the angles defined by sharp ribs with channeled inter- 

 spaces, then passing into the sculpture of the adult by successive in- 

 terpolations of secondary riblets, while the primary ribs lose in prom- 

 inence and the section of the shell becomes circular. 



Length 16.7. diam. of aperture 2.0, of apex 0.3, at middle 0.1, 

 height of arch from chord 1.8 mm. 



University of California Marine Biological Laboratory : Station 

 12, Vincente (or Redondo) Submerged Valley, Santa Monica Bay, 

 145 fathoms, temp. 45.5 F., bottom sand and mud ; also scattering 

 pecimens from station 14 off Point Fermin, 100 fathoms, temp. 

 46; station 70, La Jolla Submerged Valley, between 117 and 54 

 fathoms ; station 79, off San Diego, 64 fathoms. 



The Vincente submerged valley where this species was found in 

 considerable numbers, is one of a series of such valleys described and 

 mapped by Prof. George Davidson, of the University of California, 

 in Proc. Cal. Acad. Sci., 3 Ser. Geology, Vol. 1, No. 2. Opposite 

 Redondo the 100-fathom line marks the edge of a gently sloping, 

 ubmarine plateau which extends seaward about seven miles. Out- 

 side of this plateau the bottom descends much more abruptly. The 

 Vincente valley is nearly 300 fathoms deep and about one and one- 

 half miles wide where it breaks through the edge of the plateau. It 

 carries a depth of 100 fathoms to within one and one-half miles of 

 the beach, thus bringing the colder water of greater depths, with 

 its accompanying fauna, close inshore. It is probable that the 

 Dentalium here described will be found in deeper water as marine 

 exploration proceeds along the coast of southern California. 



The sculpture of this fine, large species recalls D. ceratum Dall 

 (Florida, Cuba, Barbados), but the former is larger, the adult shell 

 is proportionately wider, tjie young is more attenuated at the apex, 

 and the superficial striae are continued to the mouth, even on the 

 largest specimens. At the length of Dall's species, D. vallicolens is 

 more than twice as wide. The peculiar sculpture of the earlier por- 

 tion and the striation of the latter, readily separate the present 

 species from D. pretiosum and D. indianorum, even if the angled 

 apex be lost, as is almost invariably the case in the adult. Erosion 

 has in some specimens proceeded so far that patches only of the 

 outer layer of shell are left. In others it seems to have attacked the 

 shell beneath the outer layer so that longitudinal lines and encircling 

 rings of opaque white appear beneath the outer, i-hiniug layer which 

 then begins to scale off. 



