Dentalrunt.} SCAPHOPODA. 821 



Type in the Dominion Museum. 



Hab. Waikanae Beach. 



Remark. The type is no doubt a young specimen, and the Pliocene 

 shell, of which the dimensions are here given, an older shell which has 

 lost part of the posterior tube. 



Fossil in the Miocene and Pliocene. 



Subgen. 4. EPISIPHON, Pilsbry and Sharp, 1897. 



Kpisiphon, P. & S., Man. Conch. (1), xvii, 1897, 117. Type: Dentalium 

 Sowerbyi, Guilding. 



Small, very slender, rather straight shells, needle-shaped or trun- 

 cated, slightly tapering, thin and fragile, glcssy and smooth, or at 

 least without longitudinal sculpture ; apex with a projecting pipe or 

 a simple orifice ; no slit, rarely a notch. (P. & S.) 



The New Zealand species, described hereafter, demands a slight 

 modification of the above diagnosis, including forms with distinct 

 longitudinal sculpture. 



Dr. W. H. Dall writes : ' If the small end of the shell is acci- 

 dentally broken off, the animal can repair it, and in species which have 

 a simply tubular mantle and a thick shell the repairs take the shape 

 of a small tube projecting from the blunt end of the large one, as it is 

 impossible for the mantle to secrete a shell which is as large and thick 

 as the original at the point of truncation. I have examined a great 

 many Recent Dcnlalia, and have never seen a specimen in which the 

 ' tube-in-tube ' was not obviously the result of the above process, 

 and I believe it always to be so. It will be understood that it is not 

 asserted that, from a peculiar fragility or liability to transverse break- 

 age in a specjes, this condition may not be almost habitual with the 

 adults of that species ; but it is undeniable that no one has ever 

 recorded a specimen with the posterior end entirely unbroken and yet 

 possessing the supplementary tubule." (Trans. Wagner Free Inst. 

 of Sci., iii, pt. ii, 1892, 436.) 



7. Dentalium arenarium, Suter, 1907. Plate 49, fig. 16. 



Dentalium arenarium, Sut., P. Mai. S., vii, 1907, 214, pi. 18, f. 11. 



Shell arcuate, tapering, thin and shining, with a yellowish tinge. 

 Sculpture : At the apex 10 equidistant rounded longitudinal ribs, 

 which may increase to 12 or more towards the anterior end ; inter- 

 spaces distinctly longitudinally grooved, the number of these grooves 

 being 5 to 7, with minute fine somewhat irregular growth-rings. 

 When the aperture has been damaged the new growth of the shell 

 may show but traces of the costoe, being minutely reticulate. Pos- 

 terior and anterior section of shell circular. Apex with a central 

 small tube inserted in the partly closed orifice, with a slight dorsal 

 direction. 



