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NOTES ON FLANORBIS AND ITS SUBDIVISIONS. 

 By Dr. William Healey Dall. 



Read 8th May, 1908. 

 In the last number of the Proceedings of this Society there are some 

 observations by Mr. A. S. Kennard on Planorhis and some of its sub- 

 divisions, which suggest the mention of some data which have 

 accumulated since the writing of my " Land and Freshwater MoUusca 

 of Alaska." 



We have in the Jeffreys Collection, now in the U.S. National 

 Museum, his original types of P. glaher of 1834, as well as those 

 which served as the types for the " British Conchology." They are of 

 the same species, and identical with P. Icevis, Alder. Some of the 

 former are milky white, though not ' dead shells.' That Jeffreys sent 

 Alder a young P. albus by mistake for a specimen of his new species 

 does not invalidate the species. 



I have compared P. glaher with P. parvus, Say, and find that what 

 I have always regarded as the typical parvus is smaller, flatter, with 

 a more nearly circular and less oblique aperture, The vertical 

 diameter of parvus of the same size is decidedly less than in glaher. 

 But among over two hundred lots of parvus I find quite a number 

 which seem very similar to glaher, and it may be that in this country 

 we have confused the two. I have not time to study these small 

 freshwater forms, which are doubtless in need of a severe critical 

 revision. 



Mr. Kennard seems to doubt the propriety of the sections Diplodiscus 

 and Paraspira. I hold no brief for the importance of any of these 

 sections of Planorhis, but if we adopt some, in order that the divisions 

 shall be of as nearly equal weight as possible, these were needed. If 

 the whole, after due anatomical investigation, proved to be merely 

 aids for the convenient assorting of the uncomfortably large number 

 of species, I should not regret the conclusion. 



However, Diplodiscus is untenable as a Mollusc name, having been 

 used by Diesing for a worm in 1850. Von Martens in 1899 revived 

 a nomen nudum of Hartmann's Spiralina for the same group. This is 

 not Spiralina, Chaster, 1900. 



In the Nautilus for January, 1906, I have given some data for 

 forgotten Planorhis names published by Benson in 1855, some of which 

 modify my revision of 1905 in the Alaska book. One of these is 

 Omalodiscus, Benson, apparently proposed as a substitute for the pre- 

 occupied Spirorhis, Swainson, of which the type was P. rotundatus, 

 Poiret. Omalodiscus in that case would take the place of my 

 Paraspira. 



These sections may not be worth much, but if I have sinned in 

 adopting them it was in such good company as Swainson, Morch, Von 

 Martens, and Benson. If Poiret's species has got lost since Swainson's 

 time I am sorry, but American students can hardly be expected to 

 keep guard on European species, which should be herded by their 

 compatriots. 



