Contributions to the Morphology of the Group Neritacea of the Aspidobranch Gastropods.—Part II. The H elicinidæ
1911; Zoological Society of London; Volume: 81; Issue: 3 Linguagem: Inglês
10.1111/j.1096-3642.1911.tb01957.x
ISSN0370-2774
Autores Tópico(s)Fish biology, ecology, and behavior
ResumoTHE ancestral forms must have lived at a much earlier period, for Proserpina is recorded from the Kocene of the Isle of Wight, and, according to Kobelt (6), shells referable to the same genus have been found along with Helia, Planorbis, Vi alvata, and three species of Veritina inthe Lias of Somerset.There is some reason for suspecting the correctness of the identifications in the last case, and [ am unable to find any corroborative evidence of the occurrence of Proserpina in the Eocene, but the distribution of the Hydrocenids points to a geological history reaching well ' back into Tertiary times.Dawsoniella from the Carboniferous of Illinois has been attributed to the Helicinide, but I have already, in the first section of this memoir, discussed the affinities of this genus and pointed out that it must be a case of convergence.However this may be, paleontology throws very little light on the origin and distribution of existing Helicinide, and rhe 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 Antillesand the Philippines.In this, as will appear, I have been disappointed.From whatever part of the world they may come, the anatomy of the different species and even genera of Helicinidz is so closely similar that it is hard to find any difference between them.It is true that I have not been able to procure many species of Pacific Helicinide, but I have examined fairly well preserved specimens of Or -obophana, Aphanoconia, and Paleohelicina, and these three genera may be taken as typical of the more widely distributed Pacific forms.
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