50 DENTALIUM-ANTALIS. 



Dentalium cenigmaticum JORDAN, Proc. Malac. Soc. Lond., i, p. 

 264, pi. 16, f. la, Ib (July, 1895). 



From D. agile this species may be distinguished by the persistent 

 ribs which traverse the entire length of the shell, and by its some- 

 what more slender form. Herr Herman Friele informs me that Z>. 

 agile " is not always so faintly striated as described by Sars." It 

 differs from D. striolatum [occidentale~\ in its more slender form and 

 stronger sculpture ; from D. candidum in its much more slender 

 form, and in not possessing the fine transverse intercostal sculpture 

 of that species ; whilst from D. dentalis it is distinguished by its more 

 slender form, more numerous ribs (about twice as many), which are 

 thin and not well rounded as in D. dentalis, and by not having lon- 

 gitudinal microscopical striae between the ribs. 



The learned author of "British Conchology," in vol. iii, p. 197, 

 says of D. dentalis, " It has nine longitudinal ribs, besides frequently 

 a stria between each rib, but no fine impressed lines as in D. taren- 

 tinum ; " but in the specimens of D. dentalis which I have examined 

 longitudinal striae are visible ; even in specimens which appeared to 

 be destitute of them, I have with a strong lens detected them in some 

 places when holding the shell at a certain angle to the light, and in 

 many specimens these striae by their intersection with the lines of 

 growth, impart a microscopical bead-work appearance to the inter- 

 costal spaces. 



Mr. E. A Smith informs me that there are two specimens of this 

 new species in the British Museum (Natural History) from off the 

 west coast of Ireland in 1000 fms., and that he regards the species as 

 being quite recognizable. (Jordan). 



Group of D. novemcostatum. 



Shell stout and strong, moderately curved, with 9 to 13 principal 

 ribs at and near apex, and usually interstitial riblets. Apex fre- 

 quently truncate, with a small central tube. Shell often ruddy. 



Species of the Mediterranean and immediately adjacent seas, 

 mainly living at slight or moderate depths. 



With the inclusion of D. vulgare, this group would constitute the 

 genus Antalis of Stoliczka, but not the earlier Antalis Adams ; but 

 it is a matter of common observation that the apical tube is by no 

 means constantly developed in shells of any stage of growth. In the 

 following key some species of the preceding group are included. 



