DENTALIUM. 1 



Subgenus Dentalium (restricted). 



Shell prismatic or decidedly ribbed, the ribs often very strong 

 toward the apex, where there are generally from 4 to 14, but some- 

 times as many as 20. Apex with no notch or slit, or a short one. 

 I. Shell decidedly colored, generally green. 



a. Shell large, strong and stout, rapidly enlarging, the length 

 5 or 6 times the :iiameter 



Group of D. elephantinmn, p. 1. 

 a'. Shell long and slender, length 9-12 times the diameter 



Group of D. aprinum, p. 3. 

 II. Shell white or pale. 



a. 6 to about 20 ribs or riblets at apex, which is without 

 slit (though rarely with a slight notch). Circular sculp- 

 ture not conspicuously developed 



I Group of D. octangulatum, p. 5. 

 I Group of D. agassizi, p. 26. 

 a'. Shell latticed by circular lamellse or strise crossing lon- 

 gitudinal riblets Group of D. carduus, p. 29. 

 a". Square at apex, with four right angles 



Group of D. guadrapicale, p. 31. 



Group of D. elephantinum. 



Shell strong and stout, rapidly enlarging, the length 5 or 6 times 

 the diameter, with strong continuous ribs ; deeply colored. Apical 

 slit or notch small. 



The two species of this Oriental group are not verj' closely allied. 

 They differ from the groups of aprinum and octangulatum in being 

 notched or slit at the apex. 



a. Shell dark green, pale at apex, with about 10 ribs 



elephantinum, 

 h. Shell red, green and white, with 13-15 ribs formoaum. 



D. ELEPHANTINUM Linue. PI. 1, figs. 1, 2, 3, 4, 5, 6, 7. 



Shell robust, the greatest diameter somewhat less than one-sixth 

 the length, solid, strongly curved ; dark green, fading to white at 

 the anal opening. Sculpture, about 10 (9-11) strong, projecting 

 rounded longitudinal ribs, narrower than their intervals, which are 

 concave, with one or several weak, low riblets ; growth striae deli- 

 cate, inconspicuous. Aperture sub-circular, scarcely oblique, modi- 

 fied by the ribs, especially on the concave side ; anal orifice circular, 

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