412 Geological Society. 



lias become a parenchymella at the moment of fixation ; here, 

 therefore, no invagination takes phice. This, of course, 

 applies in each series only to the primitive larval forms, and 

 not to those which have been modified by tachygenesis. 

 M. Delage's remark, therefore, does not throw any particular 

 light on tiie problem of the place of the Sponges in classifica- 

 tion, and tlie terms that lie employs to de??ignate a group of 

 the animal kingdom already named by the Greeks might lead 

 to error with reference to the signification of what it has 

 been agreed to call the emhryonic Layers. 



It remains to be learnt whether the histological characters 

 have as little value as is apparently sometimes believed. 

 Remembering that the entire vegetable kingdom owes its 

 essential characters to the fact that the elements of the plant 

 shut themselves up in an envelope of cellulose, that the faculty 

 of charging themselves with chitin possessed by the free 

 region of the epithelia of Arthropods has suppressed in these 

 animals the vibratile cilia, orientated their organization in an 

 altogether peculiar direction, and justified the creation of a 

 branch for them — it will not appear to be immaterial that the 

 Sponges and the Polyps possess respectively, and each in an 

 exclusive manner as regards the other group, choanocytes or 

 nematoblasts. This is also a consequence of the properties 

 in their protoplasm. 



PROCEEDINGS OF LEARNED SOCIETIES. 



GEOLOGICAL SOCIETY. 



November 17th, ] 897.— Dr. Henry Hicks, F.R.S., 

 President, in the Chair. 



The following communication was read : — 



' Observations on the Genus Aclisina, de Koninck, with De- 

 scriptions of British Species, and of some other Carboniferous 

 Gastropoda.' By Miss J. Donald, of Carlisle. 



The Author makes some prohminary observations on the genus 

 Aclisina, and considers it advisable to regard A. pnlchra as the 

 type of the genus, wliile the so-called A. striatula must be placed 

 araono' the Miurhisonup, and A. nana is placed in a new genus. 

 The Author gives a diagnosis of Aclisina, de Kon., belonging to the 

 family Turrit ellidte, and describes the British species, twelve of 

 which are new, including two new forms placed in a subgenus. 



Of the family Murchisonidfe, and in the section AcUsoides of the 

 genus Mtiirhisonia, the form A. striatula, de Kon., and a variety are 

 described ; and a diagnosis of tlie new genus, in which A. nana of 

 de Koninck is placed, is given, followed by a description of the 

 species. 



