428 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Main fibers of the reticulum 500-850 jx thick, connectives thinner. 

 Fibers densely filled to the surface of the fiber with the longitudi- 

 nally arranged megascleres. Nevertheless the spongin uniting the 

 spicules and covering the whole bundle is sufficiently obvious in 

 preparations. All fibers alike. 



Just beneath the dermal membrane at both surfaces the megascleres 

 are gathered into long slender tracts about 50 jx thick, very different 

 in appearance from the fibers of the reticulum ; they are of the char- 

 acteristic Mycale kind, showing no or almost no spongin. These 

 tracts are obliquely tangential in position, curving to the surface 

 where they expand, forming loose brushes which also are almost 

 tangential in position. 



The megascleres are subtylostyles 300 by 6-7 jx, with many slen- 

 derer (probably younger) forms 3-4 jx thick; grouped in the fibers, 

 tracts, and surface brushes, and scattered abundantly in the paren- 

 chyma. In the type the spicules are smaller, 157-210 by 3 [x. 



The sigmas are 70-90 [x long, about 2 |x thick; abundant in paren- 

 chyma and at both surfaces. In the type they are 100 jx long. 



The palmate anisochelae are 28-30 fx long, in rosettes and singly; 

 common in parenchyma and at both surfaces. In the type they are 

 26 jx long, and do not occur in rosettes. 



Holotype.— Cut. No. 21273, U.S.N.M. 



The type is from the Sudanese Red Sea. The reticulum of fibers 

 which supports the sponge wall is irregular, not divisible into pri- 

 mary and secondary fibers, and the outer surface is rougher than in 

 the Albatross sponges. 



Mycale fistulata Hentschel (1911, p. 292), from Shark's Bay, 

 Southwest Australia, may be listed as another variety of this species. 

 The tubes approach in size the smaller Albatross specimens. They 

 fuse laterally. Thickness of wall not given, but evidently thin. 

 Small oscula are distributed over the inner surface. The skeletal 

 reticulum is regular and like that of the Albatross variety, but there 

 are no spines, the surface of the sponge being smooth. The subtylo- 

 styles are closer in length to variety regularis, but in thickness to the 

 type. Thfe anisochelae are 24r-26 [x long, the sigmas only 42-65 [x long. 



Neither Row nor Hentschel mentions ectosomal tracts and brushes 

 such as occur in the Albatross sponges. These structures have some 

 interest as representing a remnant of the characteristic Mycale skel- 

 etal arrangement, from which the reticulum of well-corn ified fibers 

 departs so widely. A reticulum of this general kind, made up of 

 cornified spiculo-fibers firmly combined, is not pecular to M. euplec- 

 tellioides. It occurs in a few other species: M. nuda (Ridley and 

 Dendy, 1887, p. 70) and M. imperfecta (Baer, 1906, p. 20). 



