392 Proceedings of the Royal Society of Victoria. 



approach those of C. guani vei-y closely in shape, indeed, were 

 shape all that we had to guide us, there would be little justi- 

 fication in separating the fossil from it. In a few cases, however, 

 traces of the sculpture of the tegmentum are preserved and this 

 enables differences of specific value to be pointed out. In C. 

 gunni the coarse grooving radiates from the apex, whereas in the 

 present species faint traces of coarse concentric sculpture are 

 visible. In this point C. pritchardi makes an approach to 0. 

 larvaeformis, as figured by Pilsbry.^ Valve VIII. (see Figs. 3 

 and 4), allowing for its worn condition, is almost identical in 

 shape with that of C. gunni, the posterior insertion plate being 

 vertical. 



Median length of specimen shown in Figs. 1 and 2, 7.5 mm., 

 breadth, 2.5 mm. Median length of original of figs. 3 and 4, 

 6.6 mm., breadth 2.5 mm., depth 1.6 mm. Length of original 

 of Figs. 5 and 6, 4.0 mm., breadth 4.0 mm. 



The resemblance of C. pritchardi to C. gunni is of considerable 

 interest since the latter species, according to the views of Pilsbry,2 

 is the most archaic of the five recent species, from the fact that 

 its posterior insertion plate is the least specialised, and approaches 

 that of the normal chitons. 



Locality.— "McDonald's," Muddy Creek. Kaliuinan (? Mio- 

 cene). Thirty examples. 



Cryptoplax gatliffi, n. sp. (PI. XXX., Figs. 7-9). 



Only a single valve has as yet came under my observation, and 

 this is imperfect anteriorly. The articulamentum is shown on 

 both sides. In shape it diflfers from any of the valves of 

 C. pritchaixli, being less pointed posteriorly. The posterior end is 

 produced downwards into a slight hook-like process, which is 

 shown in side view in Fig. 8. Viewed from below this process is 

 crescentic, as it follows the curve of the valve, and its lower 

 surface is flat. This feature, though absent from the recent 

 species and from C. pritchardi, occurs in some of the other genera 

 of Polyplacophora. 



1 Proc. Malac. Soc. 4, 1901, pi. 14, f. 12, 13. 



2 Loc. cit., p. 152. 



