136 THE SPONGES. 



them, since in the type of Desmacodcs {D. siibercus 0. Schm., 1870, p. 54) 

 the predominant megasclere is an oxea {Spindelnadel). Vosmaer hxter 

 (1885, pp. 28-29; 1887, p. 349) merged Dcsmacodes Schm. in GelUus Gray, 

 and accordingly one of Schmidt's species was designated by him Gellius 

 vagahundiis. But in Gellius (Gray, 1867, p.' 538) the megascleres are 

 diactinal, while in Schmidt's species they are tylostyles {Slecknadcln). 

 In Gellius, therefore, the sponges will not go. 



There is the more reason to follow the example of Ridley and Dendy, 

 and retain the name Desmacella for the group, of which D. vagahmida 

 Schm. and D. pitmilio Schm. serve as types, since Schmidt himself later 

 (1880, p. 82) removed D. {Hymedesmia) johnsoni (Bwk.) from the genus. 

 Moreover, Schmidt's generic diagnosis was obviously made especially to fit 

 his new species, and he refers to D. johnsoni as '' ein sich isolirt habender 

 Nebenzweig \ on Desmacella'' (1870, p. 54). Nevertheless, the case is one 

 in which the rules of nomenclature demand a new generic name, and I 

 have adopted that proposed by Thiele. 



Tylodesma alba, sp. nov. 



Plate 18, Figs. 5-7; Plate 22, Figs. 2, 3. 



Diagnosis. Sponge body massive or lamellate. . Surface differentiated into pore and 

 oscular regions, these regions occupying opposite surfaces when the body is lamellate, 

 intermingling to some extent when the body is massive. In the oscular regions the dermal 

 membrane is smooth, and imperforate save for scattered small oscula, which occur singly 

 or in groups of 2 to 4. In the pore regions the dermal membrane is rough and exhibits 

 numerous pore membranes perforated by 1 to a few pores. Sponge firm ; color of surface 



white. Spicules. Tylostyles, 1275 x 36 /x to 290 x 8 /x. Sigmaca, 64 to 22 /x long. 



Main skeleton loose, consisting of tracts of spicules and scattered spicules. Dermal 

 membrane of the smooth nonporous regions densely filled with tangentially disposed 

 tylostyles. In the rough porous regions more or less radially disposed tracts expand to 

 form superficial brushes of small tylostyles, which project beyond the surface. 



Station SJfQ5^ one entire specimen and a fragment. 



The entire specimen has roughly the shape of a truncated pyramid, 

 inverted so that the bane of the pyramid is represented by the upper 

 surface of the sponge, the truncated apex by the lower surface, which is 

 attached to conglomerate. In Fig. 7, Plate 18, the sponge is viewed 

 obli(juely so that the upper surface is plainly seen. This surface is poly- 

 gonal with six sides, longer in one direction ; unevenly concave, rising 



