112 DENTALIUM-RHABDUS. 



Easily recognized by its great length, strong curvature and bril- 

 liant polish. 



Subgenus RHABDUS Pilsbry & Sharp, 1897. 



Nearly straight or but slightly curved Dentalia, the shell very 

 thin throughout and of somewhat glassy texture when unworn ; 

 the surface brilliant, polished, without longitudinal sculpture; both 

 orifices simple, the smaller end without notch, slit or supplemental 

 tube. Type D. rectius Cpr. 



West coast of North and South America in deep water. A 

 group of more curved species from the western Pacific may also 

 form a section of this subgenus. 



Key to species. 



I. Shell with numerous annular swellings or low rings. Oriental. 

 a. Length 12-13 times the diarn., eburneum, p. 115. 



a'. Length 15 times the diam., philippinarum, p. 116. 

 II. Shell with dense, fine concentric striae ; white under a thin, 

 fugitive light chestnut cuticle ; length 45-50 mill., about 6 

 times the diam., perceptum, p. 115. 



III. Shell unsculptured, smooth, the length over 10 times the diam- 

 eter. West American. 



a. Almost perfectly straight, excessively slender, much at- 

 tenuated ; length 31'5 mill., about 19 times the diame- 

 ter, cequatorium, p. 112. 

 a. Very slightly curved, almost straight ; extremely slen- 

 der but less attenuated posteriorly ; length 29-31 mill., 

 16-19 times the diameter, watsoni, p. 113. 

 a". Very slightly curved, almost straight ; length 30-40 

 mill., 12-16 times the diameter, rectius, p. 113. 

 a'". Slightly curved, less slender; length 45-70 mill., 11- 

 14 times the diameter, dalli, p. 114. 



Group of D. rectius. 

 D. ^QUATORIUM Pilsbry & Sharp, n. sp. PL 21, fig. 43. 



Shell almost perfectly straight, excessively slender, regularly taper- 

 ing and attenuated toward the apex, thin and very fragile, transluc- 

 ent and almost colorless except where whitened by erosion. Sculpt- 

 ure none, growth-striae being nearly or quite invisible except where 

 slight surface erosion has traced them. Aperture hardly oblique, 



