ACANTHOCHITES-NOTOPLAX. 31 



middle, the plates of insertion of medium size. General color gray- 

 ish. (Blainv., Diet. Sc. Nat. xxxvi, p. 553.) 



Port of King George. 



CHITON SCABER Blainv. Body oval, elongated, a little vermiform 

 having the girdle very thick and very wide, covered with quite fine 

 hairs and small tufts. Shell small, occupying only a third of the 

 back, formed of 8 thin, fragile valves, the intermediate ones larger 

 than the terminal, exposed portion triangular and very small in 

 comparison with the plates of insertion, which are wing shaped. 

 Insertion-plate of the anterior valve especially large, 6-lobed ; that 

 of the posterior valve patelliform, with 4 lobes. General color of 

 the shell whitish gray. (Blainv., Diet. Sc. Nat. xxxvi, p. 553.) 



Seas of New Holland. 



Section Notoplax H. Adams. 



Notoplax AD., P. Z. S. 1861, p. 385 (type N. speciosa H. Ad.). 

 Macandrellus CPR. MS. in DALL, Proc. U. S. Nat. Mus. 1381, pp. 

 284, 288 (type M. plumeus Cpr.) 



Acanthochites in which the posterior valve has the insertion-plate 

 grooved outside and denticulate at the edge, between the usual two 

 latero-posterior slits. Tegmentum reduced in size by the encroach- 

 ment of the girdle at the sutures, the valves nearly or wholly 

 separated there. Anterior valve not distinctly ribbed radially, or 

 lobed around the edge. 



A rather weakly characterized section, probably artificial, but 

 decidedly convenient at present as a means of splitting the large 

 mass of Acanthochites. It is intermediate between typical Acantho- 

 chites and Oryptoconchus in characters. The girdle has the tufts 

 rather smaller than in the more typical Acanthochites, and the 

 spicular covering of the whole surface varies from nearly obsolete to 

 a dense clothing. 



The true nature of the girdle in Notoplax was not known to Dr. 

 Dall when he wrote the notes upon the group in Bull. Mus. Comp. 

 Zool. xviii, p. 417. In the typical species, N. speciosa, it exhibits 

 all the characters of the girdle of Acanthochites. There seems to be 

 no character of more than specific value separating Notoplax and 

 Macandrellus. As to Stectoplax, which Dall (I. c.) thinks may prove 

 to equal Notoplax, it is absolutely nothing but a genuine Acantho- 

 chites. 



