MUSEUM OF COMPARATIVE ZOOLOGY. 423 



Under favorable circumstances this species may be of a most brilliant milk- 

 white, but nearly all the specimens are dull ashy gray in color, even when 

 living and in perfect order. I suppose the white ones are those which happen 

 to live in pure sand, while the ordinary form comes from mud or ooze. 



Dentalium sericatum Dall. 



Plate XXVI. Fig. 1. 

 Dentalium sericatum Dall, Bull. M. C. Z., IX. p. 37, 1881. 



Habitat. Yucatan Strait, in 640 fms. 



This species is more acute than D. taphrium of the same size, and the moire 

 antique effect is of a much more prominent and zigzag pattern. In D. taphrium 

 the sculpture is also coarser. A somewhat similar effect is observable on the 

 younger portion of D. aculeatum Sowerby, which is otherwise very different. 

 The Indo-Pacific D. nebulosum Deshayes also exhibits it. The sculpture is 

 entirely independent of these differences of opacity, which at first one finds it 

 difficult to realize. 



Dentalium carduus n. s. 



Plate XXVII. Fig. 3. 



Shell pure white, sometimes attaining an ashy or rusty tinge from extra- 

 neous matter, elongated, slightly curved, and with a rasp-like surface for about 

 half its adult length; longitudinal sculpture of very numerous fine sharp raised 

 threads with somewhat wider interspaces, in which intercalary threads from 

 time to time arise; transverse sculpture of fine sharp elevated lamellse, which 

 cross the threads and become almost spinulose on the intersections; these can 

 be felt, but are almost too fine to be clearly seen with the naked eye; in the 

 perfectly adult shell, this sculpture becomes, through senility or wear, less 

 sharp on the last half of the shell; though both sorts of ridges persist, they are 

 thicker and more rounded ; shell not very thick ; aperture circular, very little 

 oblique ; anal orifice small, with a short wide slit on the convex side, and no 

 notch or wave on the other. Lon. of completely adult shell, 87.0 ; height of 

 arch from chord, 7.0; diameter of aperture, 7.0; of anal orifice, 0.7 mm. 



Habitat. Station 220, near Santa Lucia, in 116 fms., hard bottom, tempera- 

 ture 58°. 0. Station 246, in 154 fms., ooze, near Grenada, temperature 56°. 

 Also by the U. S. Fish Commission, in 338 fms., sand, at Station 2655, on the 

 Little Bahama Bank, temperature 47°.5. 



The specimen figured is only 16 mm. long, but shows sufficiently the char- 

 acters of the form and sculpture. Better specimens were afterward found in 

 some of the Fish Commission dredgings, from which the above description is 

 drawn. The peculiar sharpness felt by drawing the shell gently between the 

 finger and thumb is very recognizable, and under the glass the sculpture is 

 very beautiful. 



