4 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



allied to that of " Pisania fusiforme" . The single specimen, with 

 purpuroid operculum and radula, he called Ps. platypus. He 

 admitted that animals so different anatomically ought to be classified 

 in different " families ", not genera or species, but strangely kept 

 the same generic name for them both. 



Inspection of the excellent figures which accompany the description 

 shows at once that the radula of the purpuroid species is that of 

 Thais hcemastoma, L., which differs decisively from that of any other 

 species of Thais}- Th. hcemastoma is a common West African species, 

 occurring in almost every record of collections from Mossamedes to 

 the Mediterranean. The radula of the other species is that of a 

 Pollia, and corresponds exactly with that of P. maculosa, Lam., a 

 specimen of which from the Cape Verdes is in the G-watkin collection. 

 This latter result somewhat surprises me, for P. maculosa usually 

 possesses a shell too small to correspond in size with that of 

 M. glabella : P. variegata, Gray, or viverrata, Kien., would have better 

 fulfilled the condition of size, but the evidence of the radula is 

 decisive. The operculum of the shells with the Pisania (Pollia) 

 radula is that of Pollia, that of the shell with Th. hcemastoma radula 

 is that of Th. hcemastoma. Both Th. hcemastoma and P. maculosa 

 inhabit the rock-zone below high-water mark, where the Pseudo- 

 marginella are stated to have been found. The true M. glabella 

 were dredged in about 30 metres bottom green mud. Carriere 

 employs this difference of station to account for the divergence of 

 the two sets of forms, bat it may be doubted whether the argument 

 has any weight. 



Carriere seems scarcely to be aware of the a priori difficulty of 

 the thesis which he maintains, or of the improbability, on the face of 

 it, that three species of moUusca, which, as he admits, differ 

 essentially from one another in the anatomy of the soft parts, should 

 all be capable of secreting a precisely identical form of shell. It is 

 true that he bravely attempts to meet the obvious suggestion that 

 the negroes, who collected the shells for v. Maltzan, extracted the 

 soft parts of other mollusca and inserted them into the empty shells 

 of M. glabella. His honesty is indisputable, but it will require 

 stronger evidence than he is able to produce in order to make us 

 believe in phenomena which, if true, would revolutionize our 

 theories of development, and throw the deductions of biology into 

 confusion. 



There are three points in which Carriere's own evidence tells 

 fatally, as it seems to me, against him : (1) He says that the operculum 

 of the Pseudomarginella prevented the animal from drawing itself 

 completely into the shell, and it is obvious from his own figures 

 that the operculum could not be withdrawn within the shell's mouth. 

 He does not see that this is strong evidence that the animal does not 



1 Proc. Malac. Soc, xiii, 1919, p. 95, fig. xd (p. 90). 



