314 Transactions. 



all sides except a narrow dorsal area. The greater portion of 

 the retractor goes to the ventral side, where it forms a well- 

 defined dense mass (fig. la). Proceeding anteriorly from this 

 mass are strong widely spreading muscular bands, which en- 

 velop the ventral and lateral areas of the buccal mass. The 

 posterio - lateral attachments of the retractor muscle are con- 

 tinuous with the ventral attachment, and sweep up on to the 

 dorsal surface, when, proceeding forward, they coalesce and 

 form a thin envelope. On either side immediately above the 

 ventral muscular mass is a small area in which the constrictor 

 muscle is not enveloped by the external muscular sheath (fig. 16), 

 on each area is a well-marked flexure, which on dissection 

 proves to be the junction between the curved down and forward 

 posterior portion of the buccal mass and that immediately 

 above ; the two parts are woven together ; the odontophoral 

 cartilage and accompanying muscles curve down and terminate 

 in this area, which must be regarded as the true posterior ter- 

 mination of the buccal mass. The form of attachment of the 

 retractor muscle proves to be somewhat variable in the different 

 species. P. fumosa, Ten. -Woods,* a Tasmanian species, presents 

 a markedly different condition from what obtains in P. busbyi 

 and P. hochstetteri ; while the species under notice, though nearer 

 to the condition of the New Zealand species, forms a connecting- 

 link with P. fumosa. 



The radula is about 23 mm. in length by 5 mm. in width, 

 and is armed with 105 transverse angular rows of teeth. The 

 number of teeth per row is somewhat variable ; towards the 

 posterior end of the radula, where they form an acute angle, 

 we get the formula 66-0-66, while on the middle portion 63-0-63 

 appears to be the more usual number. Suter refers to this 

 species in his description of P. edwardi,^ and gives the formula 

 50-1-50. The absence or presence of a rachidian tooth in this 

 genus is not a matter of much importance ; in the radula before 

 me it is certainly non-existent. The tooth on either side of 

 the central cleft (fig. 3) is minute and probably functionless ; 

 the succeeding teeth large, all aculeate, gradually increasing in 

 size ; thence uniform for a considerable number, when they again 

 gradually become shorter; finally, towards the margin (fig. 4), 

 short and robust. 



The oesophagus (ces.) enters the buccal cavity in the anterior 

 third ; a salivary duct (s.a.) on either side of the oesophagus 

 empty into the cavity. The salivary glands (s.g.) are small 

 and almost completely fused together. The stomach and tract 



♦Trans. N.Z. Inst., vol. xxxvi, pp. 156-01, pi. vi, 1903, issued 1904. 

 t Proc. Mai. Soc. Lond., vol. iii, p. 290. 



