328 Dr. G. J. Allman un the Freshwater Zoophytes of Ireland. 



mens, when examined with a high magnifier, exhibit very minute 

 spiral striae. 



I have obtained two specimens from shelly sand at Tynemouth, 

 and Mr. Thompson has obligingly transmitted specimens to me 

 for examination sent to him from the west coast of Ireland. 



It has very much the general form of a Limneus, the fold on 

 the pillar adding to the resemblance. In the absence of any 

 knowledge of the animal, I have placed it provisionally in the 

 genus Odostomia, to which, among the marine mollusks, the shell 

 has the nearest affinity ; it is probable, however, that it should 

 constitute the tyjoe of a new genus. It resembles Rissoa vitrea 

 in the oblique position of the whorls, but is less cylindrical, and 

 has the body whorl much larger and more ovate. R. vitrea, though 

 described as smooth, is, when in a fresh state, more distinctly 

 striated than this species. 



XXXIX. — Synopsis of the Genera and Species of Zoophytes in- 

 habiting the Fresh Waters of Ireland. By George J. Allman, 

 M.B., M.R.C.S.I., M.R.I.A., Demonstrator of Anatomy in 

 Trinity College, Dublin *. 



The freshwater Zoophytes of Great Britain have hitherto been 

 all included under the fom* following genera, Hydra, Cristatella, 

 Alcyonella, and Plumatella. Of these. Hydra has been made to 

 include four British species, Cristatella one, Alcyonella one, and 

 Plumatella has been described as containing three species. Of 

 the above nine species I am of opinion that two must be erased, 

 viz. the Hydra ven-ucosa of Templeton, which appears identical 

 v\ ith Hydra fusca, and the Plumatella gelatinosa of Fleming, 

 which is evidently the same with Blumenbach's Tubularia Sul- 

 tana. To the seven species which now remain I am enabled to 

 add five, of which four do not appear to have been hitherto de- 

 scribed, and the other is only to be found noticed in the fauna of 

 the continent. 



This addition to the freshwater Zoophytes, by which the num- 

 ber of British species is increased more than two-thirds, re- 

 cpiires also the establishment of an additional nvmiber of genera. 

 The genus Plumatella, which was originally cstaljlished by Bosc, 

 is now made to include two forms of Zoophytes which I feel con- 

 vinced it would be better to consider generically distinct. One of 

 these forms is characterized by the tentacular disc behig cres- 

 centic and the tentacula numerous, about sixty ; the other by 

 the disc being circular and the tentacula not so numerous, from 

 twenty to thirty. The former must be retained in the genus 

 Plumatella, and it would appear that Bosc had this form alone in 



* Read at llic Mi-iliiit; ol iln- DritiKh Assoeialioii at C'ork. 



