56 RECOKDS OF THE AtJSTRAlIAN MUSEUM. 



Jackson Pholas with the figures illustrating the former (Thesaurus 

 Conchyliorum, Yol. ii., pi. ciii., ff. 12, 13, 14).* Having no 

 examples of the New Zealand species at my disposal, I am con- 

 strained to base my remarks on these engravings, which, from 

 their finish, should be faithful representations. Sowerby's mistake 

 in supposing the species to be an uiidescribed one, implies that 

 he had Gray's types before him ; while both Philippi's diagnosis 

 of P. antipodumf and Gray's description answer well to these 

 drawings and also leave no room for doubt that the specimens 

 were actually obtained in New Zealand. 



Viewed from the ventral side the difference is most apparent, 

 the gape extending a third further along the ventral margin, and 

 being much wider anteriorly in Sowerby's figure than in the local 

 species ; P. similis may be likened to a cylinder cut obliquely at 

 an angle of 30° and P. ohturamenf.um to one cut at an angle of 

 45° Dorsally the profile of the New Zealand form appears to be 

 more swollen and to taper more sharply at the anterior extremity 

 than does the Australian. The spinose ridges would seem to be more 

 feebly developed, and the size to be smaller in the local species ; 

 but, without more material for comparison, the writer would not 

 attach specific importance to such characters. The Sydney shells, 

 having been procured from sandstone rock, may reasonably be 

 supposed to be smaller and smoother than if their burrows had 

 been drilled in softer substances. 



The next ally of our species seems to be P. manilensis, Philippi, \ 

 next to that the British P. parvus, Pennant, and least of the 

 three the New Zealand P. similis. The unfigured Papuan P. 

 beccarii, Tap. Can.§, probably is akin. 



These five appear to represent a small and natural group, among 

 which the Australian species is clearly distinguishable by the 

 more anterior position of the beaks and by the less posterior 

 extension of the gape. 



This species may be characterised as follows : — 



Pholas obturamentum, sp. nov. 



Shell somewhat tongue-shaped, evenly tapering from the beaks 

 to the posterior extremity, rounded posteriorly, dorsal and ventral 

 margins straight, gibbous ventro-anteriorly, the closed valves in- 

 cluding a heart-shaped space rather longer than wide ; valves in 



* Except Philippi's Abbild. Beschr. Conch., Vol. iii., Pholas, pi. i., f. 3., 

 the other published figures, viz.. Conch. Icon., Vol. xviii., Pholas, pi. iii., 

 f. 10, and Conch. Cab. (2) Vol. xi., pt. xx., pi. vi., f. 3, are mere copies, 

 the latter a bad one, of Sowerby's f . 12. 



t Zeits. Mai. iv., 18i7, p. 71, &c. 



JThes. Conch, pi. ciii., ff. 17, 18. 



§ Ann. Mus. Civ. Geneva, vii., p. 1032. 



