42 THE VOYAGE OF H.M.S. CHALLENGER. 



in the Conch. Syst., and describes and figures Cryptoplax striatus as Chitonellus oculatus 

 in the Conch. Icon. ! 



Mr E. A. Smith 1 states that he cannot identify any specimen in the British Museum 

 with the species in question ; but two specimens, at least, from the Friendly Islands occur 

 in that collection. Mr Smith has kindly sent me a sketch of the isolated valves of one of 

 these specimens, which I find perfectly corresponds with PL III. figs. 10(X-10to of this Eeport. 



Dr P. P. Carpenter in his MS. says — " The oculatus of Reeve appears to me a distinct 

 species [from Chiton oculatus, Quoy and Gaim.]. He says nothing about pores." 



Cryptoplax burroivi (E. A. Smith) (PI. III. figs, lla-llm). 



Chitonellus larvceformis, Reeve (non Blainville), Conch. Icon., 1847, fig. 3. 



„ burrowi, E. A. Smith, Report ZooL Collect. H.M.S. "Alert," 1884, p. 85. 



Habitat. — Port Adelaide (Reeve) ; Straits of Macassar (Captain Belcher) ; Port Molle 

 (Coppinger). All in the British Museum. 



I have only to add to the description of this species, as emended by Smith, that nine 

 pores are present on the girdle on each side in the normal position. On my inquiring 

 specially on this point, Mr Smith kindly re-examined his specimens and informed me by 

 letter that " Chitonellus burrowi has pores, and is therefore a Cryptoplax. There is no 

 trace of them externally, and they are only discernible by removing the outer scaly coat ; 

 they are then seen (but not distinctly as in the other species) upon the white skin beneath 

 in just the same position and to the same numbers as in Cryptoplax larvceformis and 

 Cryptoplax striatus." 



As the existing descriptions give a sufficiently accurate and recognisable account of 

 the external appearance of the four species of Cryptoplax alluded to above, it would be 

 superfluous to re-describe them. The appearance of the detached valves has not, however, 

 been previously described, and it merits careful attention, since, as will be seen on refer- 

 ring to PI. III. figs. 9-12, each species can be readily identified by even a single isolated 

 valve. 



There is in Cryptoplax a greater dissimilarity between the intermediate valves than 

 occurs in other Chitons. In most other forms the second valve differs from the succeeding 

 by being relatively much deeper (i.e., longer), but otherwise it has the same general 

 appearance as the other valves. In Cryptoplax the first three valves are usually much 

 larger than the remainder. This is especially the case in Cryptoplax larvceformis. In 

 Cryptoplax striatus the third and succeeding valves are pretty much of the same 

 size, whereas in the other three species the last four valves are considerably smaller. 

 This statement merely refers to the exposed portion of the valves. In Cryptoplax striatus 

 all the valves may overlap or the last four may be slightly separated. The other species 



1 Report Zool Collections, H.M.S. "Alert," p. 85 



