154 PBOCEEDINGS OF THE MALACOLOGICAL SOCIETT. 



28. PLAXirnoRA petholata (Sby.). 



Chiton petholatus, Sby. : Mag. Nat. Hist., n.s., vol. iv (1840), p. 289; 



Conch. Illust., figs. 64, 65. 

 Plaxipltora fetholata, Pilsbry : Man. Conch., ser. I, vol. xiv, p. 323, 



pi. Ixviii, figs. 62-7. 



This is the commonest Chiton of the rocky portions of the South 

 Aiistralian coast-line, and it may be taken in numbers at nearly high- 

 water mark between the crevices of the rocks just as the incoming 

 tide reaches them. P. petholata attains to a large size, specimens 

 frequently measuring 95 mm. in length, by 55 in width. 



29. Plaxiphora conspeesa (Ad. & Aug.). 



Chcctopleura conspersa, Adams & Angas : Proc. Zool. Soc. 1864, 



p. 193. 

 Plaxiphora petholata var. conspersa, Pilsbry: Man. Conch., ser. I, 



vol. xiv, p. 324. 



Although not a common species, many specimens have now been 

 collected by me when in company with Mr. E. H. Matthews. They are 

 quite distinct from P. petholata in any stage of growth, and, moreover, 

 have a difi^erent habitat, for whereas P. petliolata is only taken on rocky 

 coasts on which the surf beats heavily, P. conspersa occurs in company 

 with the Ischnochitons under blocks of stone in comparatively smooth 

 water. The principal superficial differences appear to be that 

 P. conspersa is more elevated, and the lateral areas, instead of having 

 a narrow, finely corrugated, diagonal riblet, separating them from 

 the pleural tract, are defined \>j two coarsely nodulous riblets, 

 one on each side of the area, the intervening space having similar 

 sciilpturing to that on the body of the shell. Length (largest 

 specimen) 30, breadth 18 mm. 



Ilab. — "Under rocks, Port Lincoln. A beautiful and rare species" 

 (Angas) ; North Arm, Port Adelaide, on Pinna (Bednall) ; Sultana Bay, 

 Yorke Peninsula (Matthews and Bednall). In none of these localities 

 does P. petholata occur. 



Under the heading Teratology, in the Introduction to vol. xiv of the 

 Manual, p. xiii, Mr. Pilsbry writes : — " The occun-ence of six- and 

 seven-valved Chitons has been noted as early as the time of Linnaeus. 

 It is likely that the six-raked ivcre artificial fahrications, although 

 a certain number may perhaps be traced to incorrect drawings." 

 Mr. Matthews is in possession of a veritable six-valved specimen of 

 P. conspersa I 



30. Plaxiphora glauca (Quoy & Gaim.). 



Chiton fflaucus, Quoy & Gaim. : Voy. Astrolabe, Zool. iii, p. 376, 



pi. Ixxiv, figs. 7-1 1. 

 Plaxiphora e/lauca, Pilsbry : Man. Conch., ser. I, vol. xiv, p. 325, 



pi. Ixviii, figs. 68-72. 



It has been my good fortune at the last moment to become j^ossessed 

 of a specimen, although only a small one, of this species. It was 



