

i*r 



THE SPONGES. 



153 



ticulate margins. This expansion at the extreme end sometimes appears 

 rounded, and sometimes angular. The difference in appearance is probably 

 due to a difference in position, and the end is probably always angular. 

 Toward the other end the axis develops the usual thin lateral flange, 

 beyond which there is the usual incision separating the flange from the 

 large terminal plate with rounded outline and spherical curvature. The 

 denticulate plate is sometimes nearly equal in size to the larger plate. In 

 minute details the spicule differs from the very similar bipocillus of I. lamella 

 indivisus (comp. Plate 20, Fig. 15). . 



4. Anisochela, 14 /x long, Plate 19, Fig. G a. Spicule, of the palmate 

 type common in the genus, with a little spine at the smaller end. 



Skeletal Arrangement. Main skeleton consists of a uniform reticulum of 

 spinose styles. Meshes squarish or triangular. The side of a mesh is equal 

 to the length of a-single spicule, and is formed by one, two, or occasionally 

 three or four spicules. Spicules at the corners of the meshes are united 

 by spongin. 



Dermal skeleton consists of the superficial layer of the skeletal reticulum 

 and of abundant subtylotes, which are scattered irregularly, often in loose 

 tracts. 



The microscleres are abundant in the dermal membrane ; also present in 

 considerable abundance throughout the parenchyma, especially in the walls 

 of, and in the tissue immediately surrounding, the larger canals. 



Comparative. Ridley and Dencly combine (1887, p. 117), under the name 

 of Iophon paitersoni (Bwk.), a number of previously described species, and 

 record under this head specimens taken by the ■" Challenger" off the coast 



* i 



of Patagonia and Tristan da Cunha. All of these forms have palmate 

 anisochelae with pointed smaller ends, up to 30 xt long, and minute bipocilli. 

 Iophon indebitatus must be very similar, judging from Bowerbank's figures, 

 in surface appearance to one of the species combined, viz. : Halichondria 

 nigricans Bwk. (Bowerbank, 1866, pp. 266-68; Bowerbank, 1874, Plate XLV. 



Fig. 25) which occurs as a " massive " body and also incrusting. I have 



* 



examined type specimens in the British Museum of this and the other 

 Bowerbank Iophons, but the specimens are dried and old, and no longer 



permit 



studied. According to Ridley and Dendy (/. c, p. 118) in Tlalichondria 

 nigricans the spined styles measure 218 /x x 8 /x, the tylotes 195 /x by 3 /x, and 

 are thus much slenderer than in /. indentatus. 



20 



the character of the surface and the canal arrangement to be 









