SILICIOUS AND HORNY SPONGES WILSON. 455 



Genus DISCODERMIA Bocage (1869). 



Discodermia Bocage, 1869, p. 160.— Sollas, 1888, p. 292.— Thiele, 1900, 



p. 51. — Lendenfeld, 1903, p. 128. — Dendy, 1905, p. 99. — Lendenfeld, 1906, 



p. 353. 



With tetracrepid desmas; ectosomal megascleres are discotriaenes; 



microscleres are strongylate mierorhabds and larger microxeas, 



which in some species intergrade forming but one class of spicule. 



Some reference to the facts underlying the separation of Disco- 

 dermia from Theonella has already been made under Theonella. 

 It is evident that the two genera can not be sharply separated, either 

 on the score of the discotriaenes or on the possession of microxeas. 

 Nevertheless, while the two groups of species intergrade, it seems 

 advisable to retain, at least for the present, both genera. 



DISCODERMIA EMARGINATA Dendy. 



Discodermia emarginata Dendy, 1905, p. 99. 

 A single specimen from station D5414, agreeing closely with 

 Dendy's type, from the Gulf of Manaar, in respect to habitus and 

 skeleton. 



The sponge is an amorphous mass about 40 mm. in diameter, show- 

 ing low rounded protuberances. It is attached to another sponge, 

 Petrosia crustata. The consistency is dense and stony. No oscula 

 were discoverable with certainty. Doubtless they are small aper- 

 tures, more or less closed, as in the specimen of var. lamellaris (see 

 below), and so scattered as to escape observation. The pores 

 30-50 [x in diameter, are scattered over the surface, in the gaps in 

 the dermal armor formed by the overlapping disk-like cladomes of 

 the triaenes. They occur singly; or in groups of two or three, or 

 sometimes in curving rows which include a number (up to about 

 six) of pores. They open for the most part into small rounded sub- 

 dermal spaces which are independent of one another, each connect- 

 ing with the exterior by one or a few pores. 



The desmas are similar both in adult and developmental stages 

 to those described by Dendy. 



The discotriaenes are like those of the type. Diameters of the 

 cladome range commonly from 180 to 250 [jl. The spines on the 

 outer face are low and conical, disappearing near the margin of the 

 disk. The rhabdome, 80-150 y. long by 20-30 (jl thick, is pointed 

 or rounded at the apex. 



The long slender rhabds are common. They are sometimes, I 

 think always, oxeate at both ends; 5 to 8 u. thick, and in the neigh- 

 borhood of 1 mm. long. They occur in loose bundles, oblique or 



