334 HENRY CLIFDEN T.UKNUF. 



tomical details of the type of Af vodoii ta, lias also been con- 

 sulted, and, I nnderstand, lias nothing- to urgv in opposition 

 to the new arrangement. 



This alteration, together with the discovery of further 

 allied species, makes a modification of the original definition 

 desirable, and in framing it I have, for the sake of conveni- 

 ence in comparison, followed as far as possible Pilsbry's 

 definition of the section Thaumatodon as a model. 



I take this opportunity of giving a revised description and 

 new figures of a species named Trachycystis rotula by 

 Melvill and Ponsonby. A close study of this species shows 

 that it belongs to this section of Endodonta, and was 

 wrongly placed in Trachycystis. 



The specific name being pre-occupied by Hombron in the 

 sub-genus Charopa (Sec. Charopa s. s.), I propose to 

 substitute for it p erf id a, in reference to the false appearance 

 of external grooves given by the internal folds, imperfectly 

 seen through the translucent shell, as hereinafter explained. 



To Messrs. Ponsonby and Suter I am indebted for their 

 advice and help in discussing the true position of Af rodonta, 

 and to Mr. J. Farquhar and Major M. Connolly for specimens 

 for examination. 



With reference to the peculiar distribution of the toothed 

 Endodonta^ Mr. Suter has made an interesting suggestion. 



In September, 1908, on first seeing specimens of Afro- 

 donta, he wrote to me as follows : "These shells are as much 

 entitled to distinction as those of St. Helena, known as 

 Helenoconcha, though all seem to be derived from a 

 common stock. It will be remembered that in the ' Journal 

 de Conchyliologie ' ^ the late Mr. Ancey maintained that 

 Endodonta was a subantarctic genus, whilst I held that it 

 was chiefly Polynesian.- Ancey said that we could not 

 account for the occurrence of Helenoconcha on St. Helena 

 unless we admitted that they had come from the Antarctic 

 continent. The discovery of these toothed Endodontic in 



1 ' Jouni. de Concli..' vol. xlix (IftOl), p. 17. 

 - Ibid., p. 317. 



