6 THE VOYAGE OF H.M.S. CHALLENGER. 



(2.) Dentalium entalis var. agile, Sars. 



Dentalium incertum (nee. Desk), Philippi Enum. Moll. Sicil., vol. ii. p. 207, sp. S. 



„ agile, M. Sars, Rem. Forms, &c, Norway, &c, 1872, p. 31, pi. iii. figs. 4-15. 



Antalis agilis, G. O. Sars, Moll. Arct. Norv., p. 102, pi. xx. fig. 9. 

 Dentalium agile, Dall, Bull. Mus. Comp. Zool., " Blake " Dredgings, Gulf of Mexico, p. 37. 



„ ,, Gwyn Jeffreys, "Lightning" and "Porcupine" Moll., Proc. Zool. Soc. Lond., 1882, 



p. 658, sp. 6. 



Station VIII. February 12, 1873. Lat. 28° 3' 15" N., long. 17° 27' W. Gomera, 

 Canaries. 620 fathoms. Volcanic mud. 



Station 344. April 3, 1876. Lat. 7° 54' 20" S., long. 14° 28' 20" W. Ascension 

 Island. 420 fathoms. Volcanic sand. 



(3.) Dentalium entalis, var. orthrum, Watson. 



Dentalium, entalis, var. orthrum, Watson, Prelim. Report, pt. 2, Journ. Linn. Soc. Lond., vol. xiv. 



1879, p. 512. 



Station II. January 13, 1873. Lat. 38° 10' N., long. 9° 14' W. Setubal. 470 

 fathoms. Green mud. 



Station 75. July 2, 1873. Lat. 38° 38' N., long. 28° 28' 30" W. Fayal, Azores. 

 450 fathoms. Volcanic mud. 



Station 145. December 27, 1873. Lat. 46° 43' S., long. 38° 4' 30" E. Prince Edward 

 Island. 140 fathoms. Volcanic sand. 



Habitat. — The whole North Atlantic, from Davis Strait (Jeffr., 1750 fathoms) to the 

 Gulf of Mexico (Dall, 1568 fathoms), and from Spitzbergen and the Fserces to the 

 Mediterranean (Jeffr.) 



Fossil. — From the European Pliocenes north and south, in one or other of the varieties. 



The variety Dentalium orthrum is rather long and straight, and is sharply striate toward the 

 apex, thus combining the form of Dentalium agile with the sculpture of Dentalium abyssorum. 



The localities for this Dentalium are, as will be seen, remarkable ; but I believe the specimens are 

 really one species. Dr Gwyn Jeffreys having (in the Mollusca, " Lightning " and " Porcupine," loc. cit. 

 supra) recanted his opinion of the unity of Dentalium striolatum and Dentalium agile, I felt bound to 

 revise the evidence on this point before republishing the opinion I had expressed in my Preliminary 

 Report (Journ. Linn. Soc, vol. xiv., 1879, p. 513) that they should be united. The question is a 

 difficult one, and is complicated by the bad identification of specimens in cases where one would 

 expect accuracy. In the end, and for my own part, I have found it impossible to separate Dentalium 

 abyssorum, Dentalium orthrum, Dentalium agile, and Dentalium striolatum as more than varieties of 

 Dentalium entalis, Linn. With that conviction, I have not thought it necessary to spend time in 

 distinguishing the distribution of each variety in its living or fossil state ; that has been pretty fully 

 done by Dr Gwyn Jeffreys in his Mollusca of the "Lightning" and "Porcupine" Expeditions (loc. 

 cit. supra). 



