762 PROF. O. C. BOURNE ON THE 



ancestral forms must have lived at a much earlier period, for 

 Proserpina is recorded from the Eocene of the Isle of Wight, and, 

 according to Kobelt (6), shells i-eferable to the same genus have 

 been found along with Helix, Planorbis, Valvata, and three 

 species of Keritina in the Lias of Somerset. There is some reason 

 for suspecting the correctness of the identifications in the last 

 case, and I am unable to find any cori^oborative evidence of the 

 occui'rence of Proser2)ina in the Eocene, but the distribution of 

 the Hydrocenida? points to a geological hi.story reaching well 

 back into Tertiaiy times. Dawsoniella fi'om the Carboniferous of 

 Illinois has been attributed to the Helicinidfe, but I have already, 

 in the first section of this memoir, discussed the aflinities of this 

 genus and pointed out that it must be a case of convergence. 



However this may be, palaeontology throws very little light on 

 the origin and disti'ibution of existing Helicinidfe, and when I 

 began this work I hoped, not only to give a full description of the 

 anatomy of a typical member of the family, but also, by the 

 comparison of the anatomy of Pacific and West Indian forms, to 

 discover some clue to the distribution of the group with its two 

 main centres in the Antilles and the Philippines. In this, as will 

 appear, I have been disappointed. From whatever part of the 

 woild they may come, the anatomy of the different species and 

 even genera of Helicinidse is so closely similar that it is hard to 

 find any difierence between them. It is true that I have not been 

 able to procure many species of Pacific Helicinida?, but I have 

 examined fairly well preserved specimens of OrobopJiana, Aphano- 

 conia, and Pcdceohelicina, and these three genera may be taken as 

 typical of the more widely distributed Pacific forms. 



The material at my disposal w^as as follows : — 



I. Antillean forms. 



Alcadia palliata Ads. Contrivence, Waldei'ston, Jamaica. 

 Alcadia hoUandi Ads. Swing Hill, Walderston, Jamaica. 

 Lucidella aureola Fer. Bog Walk, Spanish Town, Jamaica. 

 Eittrochatella ptdchella Gray. Bog Walk, Spanish Town, 



Jamaica. 

 The above were kindly collected for me and preserved in 

 Perenyi's fluid by Mrs. G. B. LongstaflP, F.L.S. 



II. Pacific, Australian, and Indian forms. 



Aphanoconia goiddiana Forbes, from Torres Straits : for 

 specimens of this species I am again indebted to Mrs. 

 LongstaflT, who procured them for me from Mr. 0. Hedley, 

 of the N.S. Wales Museum. 



Aphanoconia andamanica Benson. 

 Aphanoconia merguiensis Pfeiflfer. 

 Aphanoconia rogersii, sp. n. 



These three species are from the British Museum and formed 

 part of the collection made in the Andaman Islands by Mr. G. Rogei-s. 



