ELASMOSTOMA. — EAPHIDONEMA. 197 



is smooth, with minute circular apertures about '3 mm. in width, and from '6 to 

 1 mm. apart ; the interspaces are perforated with minute puncta. The inner surface 

 exhibits reticulate fibres so closely disposed that the interspaces can scarcely be 

 distinguished without a lens. 



As seen in a microscopic section, the fibres are from "1 to '2 mm. in thickness ; the 

 spicular structure is very indistinct, but it appears to resemble that of E. scitulum. 



The ibrm figured by Goldfuss is stated to have been derived from Essen ; but, as 

 Geinitz has pointed out, this is an error, and there is no doubt that it came from 

 Maestri cht, where these small sponges appear to be fairly abundant. 



Distribution. Upper Chalk : Maestricht. 



Genus EAPHIDONEMA, Ilinde, n. g. 



Sponges cup- or funnel-shaped, or forming convolute expansions. On one surface 

 of the wall, and in some forms on both, there is a modified dermal layer, either 

 compact or minutely porous. The dermal layer, either on the outer or inner surface 

 of the wall, is perforated with oscular apertures, except in one species in which it 

 has no oscular apertures, though it extends over the canal apertures of the wall. 

 Definite canals are usually present ; they penetrate the wall from one or both surfaces, 

 and in some instances extend quite through it. 



The fibres are composed of filiform three-rayed spicules similar to those o^Corynella ; 

 the basal ray of the spicules is but very slightly developed, so that in microscopic 

 sections they appear for the most part as simple uniaxial forms. Rarely are larger 

 three-rayed spicules to be seen in the fibres, though such may be present in the 

 dermal layer, the minute structure of which I have not been able to determine. 



As already mentioned, this genus resembles Elasmostoma in its mode of growth 

 and general structure, but the spicular constitution of the fibres is of a different 

 character, and resembles the Corynella type. It also includes some of the species on 

 which Prof. Sollas has based the genus Catagma, but the characters assigned to this 

 genus are not sufficiently definite, and its spicular structure, judging from the figures 

 and descriptions, is very different from that of Bap hidonema, and resembles somewhat 

 that of Elasmostoma. 



Raphidonema contortum, Hinde, n. sp. (Plate XXXVII. figs. 2, 2 a, 2 b.) 

 1874. Manon peziza, Davey, Trans. Newbury Field-Club, p. 10. 

 Sponges growing in convolute expansions ; the folds of the walls frequently coalesce 

 so as to form intricate masses of considerable size. The sponge is usually attached 

 by its base, not infrequently to a sponge of a different species. A small example is 

 29 mm. in height by 42 in width, whilst a fairly large specimen is 65 mm. in height 

 by 100 in breadth. The walls are from 4 to 6 mm. in thickness. Both surfaces are, 

 in the best-preserved specimens, smooth, and alike covered with a modified dermal 



