MR. S. O. RIDLEY ON THE GENUS ECHTNODTCTYUM. 493 



Part III. 



On some Sponges of the Order Echinonemata. 



By S. O. Ridley. 



The concluding part of this paper deals with an hitherto un- 

 recognized generic type, which may be assigned to the 



Order ECHINONEMATA, Carter. 



Family Axinellida, Carter. 



Group Multiformta, Carter. 



Echinodictyum *, n. gen. — Sponge erect; cup-shaped or ramose. 

 Skeleton formed of spicules united into distinct coherent fibres. From the 

 fibre project at right angles short strongly-spined cylindrical spicules 

 tapering from their attached ends. Spicules of fibre smooth, acerate 

 (doubly pointed). No special flesh-spicules. 



Type Spongia bilamellala, Lamarck, Ann. Mus. Hist. Nat. xx. p. 434. 

 Obs. The nearest affinities of this genus appear to be with 

 Dictyocylindrus, Bowerbank, s. str., i.e. with those species which 

 have a more or less distinct firmer axis and echinated fibre, com- 

 bined with a spiculation of smooth acuates and acerates in the fibre, 

 smooth acuates and spined cylindrical, or blunt acuates echinating 

 it, and no minute flesh-spicules (e.g. Dictyocylindrus hispidws, 

 Bowk., Axinella damicornis, Schmidt, D. Pykei and laciniatus, 

 Carter). It differs from Dictyocylindrus mainly in the abseuce of 

 the smooth acuates, usually so abundant in that genus, and in the 

 much greater defiuiteness of the fibre. It perhaps connects 

 Dictyocylindrus by these characters with the Ectyonida (Carter). 



As the typical species has never been described from a micro- 

 scopic examination or figured, and as such fine specimens are 

 available, I append a full description with figures. 



Echinodictyum eilamellatum. (Plate XXVIII. figs. 1-6.) 

 Spongia bilamellata, Lamarck, Ann. Mus. Hist. Nat. xx. p. 434 ; 



Anim. s. Vert. (2) ii. p. 556. 

 Sponge erect, turbinate, expanded, or compressed ; the margin 

 of the cup is prolonged in adult specimens into one or more 

 broad expansions ; a short pedicel. Internal surface of cup 

 smooth (occasionally undulating), bearing the numerous scattered 

 vents. External surface exfoliating so as to form obscure longi- 

 tudinal ridges, which, together with the intermediate spaces, grow 

 out into larger or smaller rounded excrescences, composed of 

 reticulate fibrous tissue. Texture of inner surface dense, that of 

 outer loose ; in dry state firm, subelastic. Colour in dry state 

 pale brown. 



* exTvos, a sea-urchin or hedgehog, and (~ncrvov, a net. 



