1894.] NATURAL SCIENCES OF PHILADELPHIA. 75 



3. Degree of differentiation of dorsal areas, ^vhich may be either 

 raised at the edges, or coutinuou? with the side areas, and eithe7' 

 transversehj or longitiidinalhj striated. Sculpture of side-areas, and 

 shape of the pustules, which may be either convex or concave. 



The preceding features may be deserved without disarticulating 

 the specimen; the following require its dissection, which is easy 

 enough after soaking it in warm water. 



4. Shape of tegmentum of tail valve, proportion of its breadth to 

 length, and position of mucro. 



5. Shape of j)osterior insertion-plate of tail valve, which may be 

 either regularly rounded or angular. Number of slits. 



6. Length of front slope of tegmentum of head valve as compared 

 with length from apex to edge of front teeth of same. 



The last mentioned character is a good index to the degree of im- 

 mersion of the valves in the girdle. Of course, any of these charac- 

 ters is subject to individual variation, but if a description is prepared 

 noticing them all, it is extremely likely to contain something which 

 will lead to the identification of a given specimen. In my account 

 of this genus in the Manual of Conchology, insufficient attention was 

 given to the features of the tail valve. 



The following species referable to the family Acanthochitidce have 

 been described from Australia: 



1825. — Chiton pohjchetus Blainville, Diet. Sci. Nat., XXXVI, p. 



552, New Holland. 

 1825. — Chiton roseiis Blainville, t. c, p. 553, New Holland. 

 1825. — " Sueurii " " " King George Sound. 



1825. — " scaber " " " Seas of New Holland. 



1861. — Criiptoplax {Notoplax) speriosa H. Adams, Proc. Zool. Soc. 



Lond., p. 385, Tasmania (Cuming); Flinder's I. (Mil- 



ligan). 

 1864. — Hanleya variabilis H. Adams & G. F. Angas, P. Z. S. p. 



194. Yorke Peninsula (Angas). 

 1864. — Acanthochites carinatns H. Adams & G. F. Angas, P. Z. S. 



p. 194. Port Jackson (Angas). 

 1864. — Acanthochites costatii^ H. Adams & G. F. Angas, P. Z. S. 



p. 194. Port Jackson (Angas). 

 1865. — Acanthochites sciitiger A. Ad. ii- Eve., Angas, P. Z. S. p. 



188. Port Lincoln (Angas). 

 l^H2.—Acaidhoc]iifes tristis Rochebrune, Bull. Soc. Philomath. 



Paris, 1881-1.SS2, p. 194. New Holland (Dussumier). 

 1882. — AcanthochitcK tnrgidiis Rochebrune t. c, p. 194. New 



Holland (Peron & Lesueur). 



