IREDA.LE : NOTES ON POLTPLACOPHORA. 129 



Moreover, it would seem that Blainville himself got disgusted at 

 the treatment of his genus, as in his monumental monograph on the 

 Chitons in the Diet. Sci. Nat. (Levrault), vol. xxxvi, p. 519 et seq., 

 1825, he discarded it, and included the species in the genus Chiton, 

 but once again changing their names. Here, on p. 553, Chiton 

 vei'miformis, Blainville = Cryptoplax larviforniis of seven years 

 earlier, and Chiton leachi, Blainville = Cryptoplax deiJressus of seven 

 years previous. Pilsbry preferred Acanthochites, liisso, 1826, to 

 Cryptoconchufi, Guilding, 1829, and based his family name on that, 

 separating the Cryptoplax species into a separate family, Cryptoplacidse. 

 Thiele has amalgamated these two families, ranking them as sub- 

 families only, and using the name Cryptoplacidte on account of the 

 earlier introduction of the genus-name Cryptoplax . 



The conclusion that Cryptoconchns must date from 1815 makes this 

 the oldest genus-name, and consequently the family name would 

 become Cryptoconchidoe. I am at present inclined to agree with 

 Thiele that Cryptoplax is not able to be considered as separable as 

 a family. 



The genus-name Macandrellus. 



This name was introduced ex Carpenter's MS. by Dall in the 

 Proc. U.S. Kat. Mus., vol. i, p. 299, 1878, where the type is 

 designated as Macandrellus costatus, Adams & Angas. Pilsbry 

 rejected it in the Man. Conch., vol. xv, p. 32, 1893, as Dall's genus 

 was not the same as that of Carpenter, and also " The first use of the 

 name (as above) being unaccompanied by a diagnosis must fall". In 

 my investigations I constantly meet with such statements by authors, 

 and Dall wrote (Journ. Conch., vol. xi, p. 294, 1906), "It is an 

 unfortunate fact that the abrogation of the original rule requiring 

 a diagnosis to validate a genus." I will admit there may have been 

 such a rule, but the abrogation appears to have been useful as long 

 ago as 1847, and probablj^ earlier. For we have Gray in the Proc. 

 Zool. Soc, 1847, when he drew up liis epoch - marking "List 

 of the Genera of Recent MoUusca, their Synonyma and Types", 

 introducing new generic names without a diagnosis. We liave the 

 commonly utilized Catal. Yoldi Collection, 1853, by Morch, and 

 1 note Fischer in his Man. Conch, in 1880-7 also indulging in 

 the same practice ; this is only to quote the very first works that 

 occur to n;emory. Judging from llisso's genera, where the generic 

 diagnosis disagrees with the identifications of the species named, 

 it would have been better had the abrogation commenced earlier. 



To come back to Alacandrelliis, there is now no lawful reason for its 

 non-acceptance, and it must replace the name Loboplax, Pilsbry, 

 introduced in the Nautilus, vol. vii, p. 32, 1893, with Chiton violaceus, 

 Quoy & Gaimard, cited as type. This species and Adams and 

 Angas' costatns are undoubtedly congeneric in the strictest restriction. 



In my paper in these Proceedings (vol. ix, p. 101, 1910) I noted 

 the extreme diificulty of determining the divisions of Acanthochites. 

 I showed Thiele had been puzzled, and admitted my own difficulties. 

 I, from further studj', now consider the admission of the following 



