322 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



It is interesting to note the analogy presented b}' other limaciform 

 MoUusca, in which the shell, once probably external and substantial, 

 has become overlapped by developments of the dorsal area and has 

 gradually disappeared from view, ultimately eitlier vanisliing alto- 

 gether or becoming disintegrated, or else, as in the case of Testacella, 

 completely shifting its position or becoming redeveloped in a position 

 where a special necessity had to be provided for. In all tliese cases 

 it will be found that the modification of tlie size or shape of the 

 shell was, as it were, compensated for by a corresponding modification 

 of the integument, which took its place and did its work. 



It is possible that future discovery may bring to light a form or 

 forms of Chiton in which the process of degradation lias proceeded 

 further still, and in which all the valves are markedly embedded, or 

 in which some have even become non-existent. On a consideration 

 of the present species and its nearest allies, one would expect the 

 sixth, fifth, and fourth valves to disappear first, since in their case 

 the reduction of size has proceeded furtliest, while one might hazard 

 a conjecture that the limit valves at either end would maintain their 

 existence longest. 



Mr. C. Hedley records ' no Polyplacophora from the atoll, with the 

 exception of a single mutilated median valve of a species of Tonicia, 

 dredged at 150 fathoms. He remarks that Pease only knew of six 

 species of Polyplacophora from the Central Pacific, a fact remarkable 

 when it is considered how abundantly the group is represented on the 

 west coast of South America, Australia, and New Zealand. 



^ " The Mollusca of Funafuti," Supplement : Mem. Anstr. Museum, iii, pt. ix, 

 p. 550, 1899. 



