476 ME. S. O. RIDLEY ON THE GENUS DIRRHOPALUM. 



On the Genus Plocamia, Schmidt, and on some other Sponges of 

 the Order Echinonehata. By Stuart 0. Eidlet, M.A., 

 E.L.S. With Descriptions of two additional new Species 

 of Dirrhopalum by Prof. P. Martin Duncan, M.E. Lond., 

 E.E.S., E.L.S., &c. 



[Bead June 2, 1881.] 

 (Plates XXVIII. & XXIX.) 



Part I. 



Introductory Remarks, and Descriptions of Species of Dirrhopalum. 



By S. 0. Eidlet. 



Although the genus Plocamia was only recognized as a distinct 

 type in the year 1870 *, it now proves to be one of the most 

 widely distributed, as well as one of the most beautiful, of the 

 now numerous genera of the interesting order to which it belongs. 

 Hitherto only three species have been assigned to it, viz. : — 



Plocamia gymnazusa, Schmidt, Spong. atl. Geb. p. 62, pi. iv. fig. 18. 

 Cuba, 270 fathoms. 



P. clopetaria, Schmidt, I. c. p. 63, pi. iv. fig. 17- Florida, 195 fathoms. 



P. plena, Sollas, Ann. & Mag. N. H. (5) iv. p. 44, pi. vi. W. Africa, 

 Lat. 15° S. Depth ? 



In the present paper I have described f a new species from 

 New Zealand, and given annotations on others previously de- 

 scribed under other generic names ; the latter are known, one 

 from Ireland, another from Ceylon, and another from Cape 

 St. Vincent. 



No species has been described from the Arctic regions ; but 

 Ehrenberg (Zweite deutsche Nordpolarfahrt, pi. iv. fig. 8) figures 

 from the sea in the neighbourhood of either Spitzbergen or East 

 Greenland a cylindrical spicule, entirely spined, arcuately curved, 

 slightly enlarged at the ends, which probably belongs to an un- 

 known species allied to Dirrhopalum (Hymeraphia) microcionides, 

 Carter. Ehrenberg names the spicule Amphidiscus anceps. 



The distribution of the genus is thus now seen to extend from 

 the Equatorial Atlantic to the South Pacific Ocean, and into the 

 Indian Ocean and North Atlantic. 



* O. Schmidt, Spong. atl. Geb. p. 62. 



t Note. — The terminology here adopted is, in general, that of Mr. Carter 

 (Ann. & Mag. N. H. (4) xvi. p. 1 &c). Measurements of spicules are the 

 average maximum measurements ; the diameters given are the greatest diameters 

 of the spicules. 



