314 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



In the adult sterraster, the outer ends of the rays are stellate — viz. 

 polygonal and very distinctly produced at the angles into sharp little 

 processes (spines of Sollas) ; the outer ends about 4 \i in greatest 

 diameter and closely set. Hilum, a depression, as usual showing no 

 rays. Young stages of the sterraster are plentiful in the choanosome. 

 They show that the ontogenetic development of the spicule takes 

 place in the usual way (Sollas, 1888, p. lxiv). 



7. Dermal oxyaster (pi. 46, fig. 4, a) ; total diameter 4-6 jjl. With 

 a perceptible centrum; number of rays rather small, about five seen 

 in optical section. Very abundant in the dermal membrane of both 

 surfaces. Abundant also in the ectochrote and through the 

 choanosome. 



8. Choanosomal oxyaster (pi. 46, fig. 4, b). Total diameter, 

 24-36 [x. Rays long, strong, tapering, more or less distinctly, though 

 minutely, spinose at the end. The spicule is sometimes classifiable as 

 an acanthtylaster of Lendenfeld, but again the rays are really 

 pointed at the end. Total number of rays 6 or 7 to about 20, 5-10 

 visible when the equator of spicule is focussed. Centrum absent in 

 spicules with smallest number of rays; distinctly developed in spic- 

 ules with largest number of rays. Size of the spicule is, as usual, 

 inversely as the number of rays. Abundant in the choanosome. 



Eolotype.— Cat. No. 21320, U.S.N.M. 

 « 



GEODIA SPARSA, new species. 



Plate 37, fig. 5 ; plate 46, figs. 7, 8. 



A fragmentary specimen, from station D5593, chiefly consisting of 

 two subcylindrical branches, largely fused together, but projecting 

 at the top as free and somewhat flattened lobes rounded terminally. 

 Total height 70 mm., greatest width 40 mm., diameter of the branches 

 from 15 to 25 mm. 



Color of surface and cortex, pale reddish; that of choanosome a 

 light yellowish brown. The cortex is 1.5-2 mm. thick, and is occu- 

 pied almost entirely by the sterrastral layer. The choanosome is ex- 

 cavated by numerous canals, 2-3 mm. in diameter, extending more 

 or less lengthwise through the branches. 



The surface is now, in general, glabrous. But in protected places 

 there are spicules that project 1-3 mm. These, in such places, are 

 abundant, yet not abundant enough to constitute a spicule-fur. 



The dermal membrane with its crust of minute oxyasters is intact, 

 but there are no apertures visible to the eye. The only apertures are 

 minute pores, about 16 \i in diameter, scattered over the general 

 surface; not anatomically distinguishable into afferent and efferent, 

 although some are doubtless of the one kind, some of the other. 



