Miscellaneous. 413 



(' Gcbiss,' vol. ii. p. 340) has mistranslated me to the extent of 

 saying that I have regarded the Acmaeida^ as the most " primitive " 

 group, in opposition to my earlier views, which is quite inaccurate. 

 I have, iu the ' Blake Gastropods ' (pp. 43G, 437), shown whj^ the 

 Patellida3 may reasonably be regarded as derived from Acma;idae, the 

 original ctenidia having been wholly lost. The row of lamellae 

 within the mantle-edge have taken up the branchial function, and 

 iu some species, as in Ancistomesus, become arborescent proliferations. 

 The branchial cordon is occasional in Acmaeidje — I have seen it 

 complete in Scurna mesoleuca ; it is present, but incomplete, in the 

 common Lottia gigantea of California ; and, even if Dr. Thiele was 

 correct iu supposing that it was absent in Scurria scurra, there 

 would still be no ground for his conclusion that its absence in the 

 latter species indicates a failure of the grounds upon which I united 

 in one group, as Proteobranchiata, the Acmaeida) and PatelHdae. 



But there is excellent reason for believing Dr. Thiele to have been 

 misled by an exceptionally contracted specimen of Scurria scurra 

 and to be entirely wrong in his conclusion that the species is without 

 a branchial cordon. The latter is figured and described by d'Or- 

 bigny from living specimens (Am. Mer. p. 478, pi. Ixiv. figs. 11-14). 

 I have seen sketches by Couthouy made from life fully confirming 

 d'Orbigny, and, lastly, I have seen, but do not now remember where, 

 an alcoholic specimen which showed them clearly. Dr. Thiele's 

 specimen only appeared " etwas wulstig,'' somewhat pufted up, in 

 the place where the cordon should be ; but there can be no doubt 

 that this pufiing up simply represented the alcoholically-contracted 

 lamellce of the cordon, rendered indistinct by improper preparation. 



Many of the minor details in which Dr. Thiele's observations 

 differ from mine may be reasonably explained by the variation which 

 is exhibited by individuals ; and my chief criticism upon what is, in 

 the main, a praiseworthy and useful work is that Dr. Thiele has 

 failed to take account of this factor, which more extensive expe- 

 rience with the radula of a single species would have undoubtedly 

 revealed to him. The result has been, not only has he estimated 

 too highly the constancy of minor details of the radula in single 

 species, but he has made an excessivenumber of so-called "generic" 

 distinctions, the names of which in many eases will simply enlarge 

 our catalogues of synonyms. 



In conclusion, I may point out that the relations of the radula in 

 LepetelJa to that of Le2>eta, &c., offer additional reasons for thinking 

 that the Lepctidae are of the limpets those most nearly alhed to 

 normal or more usual types of Gastropods, and also that the simi- 

 larity of the shell of the Silurian TryhlidUnn to that of some recent 

 limpets (Olana &c.) by no means authorizes us to conclude that the 

 soft parts of TryhUdium were also similar to those of recent Patcl- 

 lidae. Indeed, when the almost incalculable length of time inter- 

 vening between our days and the Silurian is considered, together 



Ann. & Mag. N. Hist. Ser. 6. Vol. xii. 31 



