286 PROCEEDINGS OF THE ACADEMY OF [1893. 



remain in any of the three groups, and whether most ancient or not, 

 so far as these characters go the Lepetidce are nearest to the Proto- 

 limpet. 



In my work on the Blake Mollusks (II, p. 436) I said that J.cmcc- 

 idce, of all the groups of Docoglossa, is the most typical ; that is, 

 within the limits of that family are found assembled, sometimes in 

 one and the same animal, the greatest number of organs which taken 

 singly are characteristic of Docoglossa. This is strictly true, but Dr. 

 Thiele (Gebiss, p. 340, vol. II) has mistranslated me to the extent of 

 saying that I have regarded the Acmceidce as the most " primitive" 

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

 I have in the Blake Gastropods (p. 436-7) shown why the Patellidce 

 may reasonably be regarded as derived from Acmceidce, the original 

 ctenidia having been wholly lost. The row of lamella? within the 

 mantle edge have taken up the branchial function and in some 

 species, as in Aneistomestts, become arborescent proliferations. The 

 branchial cordon is occasional in Acmceidce, I have seen it complete 

 in Scurria mesoleuca ; it is present but incomplete in the common 

 Lottia gigantea of California ; and even if Dr. Thiele was correct in 

 supposing that it was absent in Scurria scurra there would still be no 

 ground for his conclusion that its absence in the latter species indi- 

 cates a failure of the grounds upon which I united in one group, as 

 Proteobrancliiata, the Acmwidce and Patellidce. 



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 Orbigny 

 from living specimens (Am. Mer., p. 478, pi. 64, figs. 11-14). I 

 have seen sketches by Couthouy made from life fully confirming 

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

 alcoholic specimen which showed them clearly. Dr. Thiele's spec- 

 imen only appeared " etwas wulstig," somewhat puffed up, in the 

 place where the cordon should be, but there can be no doubt that 

 this puffing up simply represented the alcoholically contracted 

 lamella? 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 experience 



