REPORT ON THE MONAXONIDA. 117 



occasionally assume a definite shape, as in lophon 2yiceum, Vosmaer, which is cup-shaped, 

 and in Io2:>hon cylindricus, nobis, which is cylindrical. A common feature of the 

 genus is the distinctness of the dermal membrane and pores. 



Of the spicules the most remarkable are the bipocilli, which are, so far as we are 

 aware, confined to the genus. 



The genus has a wide distribution, as will be seen by reference to the localities 

 given for the various species, of which six were obtained by the Challenger. 



lophon pattersoni, Bowerbank, sp. 



1866. Halichondria Patteisoni, Bowertank, Mort. Brit. Spong., vol. ii. p. 255; vol. iii. 



p. 115, pi. xlvi. 

 •1866. Halichondria scandens, Bowerbank, Mon. Brit. Spong., vol. ii. p. 259; vol. iii. 



p. 112, pi. xlv. 

 1866. Halichondria Hyndmani, Bowerbank, Mon. Brit. Spong., vol. ii. p. 264 ; vol. iii. 



p. 115, pi. xlvi. 



1866. Halkltomlria nigricans, Bowerbank, Mon. Brit. Spong., vol. ii. p. 266; vol. iii. 



p. 113, pi. xlv. 



1867. Alehion hijndmani, Gray, Proc. Zool. Soc. Lond., May 1867, p. 534. 

 1867. lophon scandens, Gray, Proc. ZooL Soc. Lond., May 1867, p. 534. 

 1867. lophon nigricans, Gray, Proc. Zool. Soc. Lond., May 1867, p. 534. 

 1880. Esperia Pattersoni, Vosmaer, Notes from lieyden Museum, vol. ii. p 143. 

 1880. Esperia Hyrulmani, Vosmaer, Notes from Leyden Museum, vol. ii. p. 144. 

 1880. Esperia scandens, Vosmaer, Notes from Leyden Museum, vol. ii. p. 144. 



1880. Esperia nigricans, Vosmaer, Notes from Leyden Museum, vol. ii. p. 144. 



1881. AleUon proxinmm, Ridley, Proc. ZooL Soc. Lond., January 1881, p. 117. 



Sponge massive, amorphous, crumbling. Colour dark brown. Surface uneven, 

 corrugated^ 



The skeleton consists of (1) a dermal layer of long, dumb-bell-shaped spicules (tylota) 

 with the knobs u.sually slightly spined and the shaft smooth. (2) A rather loose 

 reticulation of spined stylote spicules penetrating all through the body. Two kinds of 

 microsclera are present; (l) palmate anisochelse, with pointed smaller ends, very fine, 

 measuring up to 0"03 mm. long. (2) Minute bipocilli. Both of these vary greatly 

 in numbers in difi'erent specimens, and in diflerent parts of the same specimen. For 

 measurements of the styli and tylota see the table given below. 



The Challenger specimens of lophon from Stations 308, 311, and from Tristan da 

 Cunha form connecting links between several previously known, though Hi-defined, forms. 

 We are thus enabled to unite these several forms as varieties of a single sjjecies. In 

 all of them the external appearance seems to be the same, and the distinction has lain 

 chiefly in slight variations in form and size of the spined styli and of the tylota {vide 

 table below). The microsclera vary considerably in the numbers in which they occur, 

 but this cannot be considered as a specific distinction. We thus have a single species 



