74 PROCEEDINGS OF THE ACADEMY OF [1894. 



sculpture of tlie valves, which is not paralleled by any other small 

 Chitou of Australian waters. 



Another species referred to this genus, Call ido chit on Coppijigeri'E. 

 A. Sniitli, lias been described from Port Jackson. I have not seen 

 the type, liut I believe it to be a young, roughly sculptured Isch- 

 nochlton fndicosus Gld. 



Family MOPALIID^. 



Genus PLAXIPHOEA Gray. 



Plaxiphora petliolata Sowb. 



Abundant and typical at Port Jackson and Port Hacking. At 

 the latter locality some specimens occurred having the exterior coloi'ed 

 like P. glaiiut Quoy (Man. Conch., XIV, pi. 68, fig. 72j, and 

 the inside pink and white, slightly clouded with blue. I have not 

 seen specimens of the true P. (jlatica, which is described as smooth 

 outside. The valves of P. petholata are always finely corrugated. 



Family ACANTHOCHITID^. 



But one genus of this family, A<nntJtochltes, has been found to 

 have representatives in Australian waters. This genus is nearly 

 world-wide in distriliution in tropical and temperate seas. The other 

 genera of the family are local in distribution, and contain very few 

 species. 



Genus ACANTHOCHITES Risso. 



The genus Acantltochlte.^ is one of the most difficult groups ot 

 Chitons, partly on account of the insufficiency of the published 

 descriptions of species, partly because the specific characters are not 

 easy to see in the creatures themselves, especially if the external 

 features only of the animal are studied. 



When the valves are removed from the girdle, a number of ex- 

 cellent distinguishing characters are seen, enabling us to reach more 

 satisfactory conclusions in most cases. 



The characters to be especially observed are : — 



1. General form, etc., features of girdle, its tufts, and presence or 

 absence of a marginal fringe of longer spicules. 



2. General features and coloring of valves; shape of iheir poderlor 

 (sutirral) margin^, which may be either concave, or convex and 

 strongly imbricating. 



