Dentalium.] SCAPHOPODA. 819 



numerous longitudinal riblets. The apical slit is a frequent but by no 

 means invariable feature, being here an extremely mutable character, 

 as in most other groups of the genus. 



KEY TO SPECIES. 



A. Shell nearly straight, rapidly tapering . . opacum. 



B. Shell moderately curved posteriorly, slowly tapering . . . . zelandicum. 



3. Dentalium opacum, Sowerby, 1828. 



Dentalium opacum, Sow., Zool. Journ., iv, 1828, 198; Man. Conch. (1), 

 xvii, 70. ? D. conicum, Hutton, C. Tert. M., 1873, 1 ; Plioc. M., 73, 



pi. 8, f. 77. 



Shell nearly straight, attenuated at the apex, its diameter increas- 

 ing much more lapidly than in the other species ; with 17 or 18 rather 

 blunt longitudinal ribs, with a smaller one between each ; all the ribs 

 nearly obsolete at the wider extremity ; posterior fissure short, dorsal. 

 (Sowerby.) 



Length, 63-75 mm. ; diameter, 7-5 mm. 



Type in the British Museum ; of D. conicum, from the Miocene, in 

 the Dominion Museum, Wellington. 



Hob. Chatham Islands ; one specimen in the Canterbury Museum. 

 Christchurch. 



Fossil. D. conicum. in the Miocene and Pliocene. 



Remarks. It seems to me highly probable that Mutton's species 

 is a synonym of D. opacum, Sowerby. Of the latter, a few specimens 

 were preserved in Mr. G. Humphrey's collection, with the following 

 label : " White striated elephants teeth, per S. Sea ships, supposed 

 New Zealand." 



4. Dentalium zelandicum, Sowerby, 1860. Plate 49, fig. 14. 



Dentalium zelandicum, Sow., Thes. Conch., iii, 1860, 101, pi. 223, f. 13 ; 

 Conch. Icon., xviii, pi. 2, f. 8 ; Man. Conch. (1), xvii, 70, pi. 6, f. 81 ; 

 Murdoch and Suter, T.N.Z.I., xxxviii, 303. D. pacificum, Hutton, 

 C.M.M., 1873, 5 ; M.N.Z.M., 130 ; Man. Conch. (1), xvii, 70. 



Shell large, slightly arcuate, rather slowly tapering, with nume- 

 rous unequal ribs ; apex mostly with a slit. Sculpture : There are 

 narrow, but little raised longitudinal ribs of unequal strength, 18 to 

 20 at the posterior end, 30 to 45 at the anterior extremity, about 20 

 of which are stronger than the others ; they are crossed by distinct 

 dense oblique growth-lines. Colour white, banded with pale grey and 

 tawny. Posterior orifice narrow, circular, sometimes with a ventral 

 fissure, which is simple, narrow, and about 4 mm. long. Aperture 

 oblique, the dorsal lip somewhat advancing, circular, peristome thin 

 and sharp. 



Length, 57 mm. ; greatest diameter, 8 mm. (from Sowerby's 

 figure). Length, 61 mm. ; posterior diameter, 1 mm. ; anterior dia- 

 meter. 7-9 mm. 



