1887.] NATURAL SCIENCES OF PHILADELPHIA. 237 



each case being terminated by long, hooked rays, while the rotules 

 of the others are larger, flatter and more delicately divided. (PI. XI.) 



KEY TO THE. SPECIES OF THE GENUS HeTEROMEYENIA. 



1. Rays of long birotulates noticeably incurved like fish-hooks ; 

 rotulffi of shorter class mushroom shaj^ed ; shafts generally 

 smooth. Dermal spicules present. (PL XI, fig. iii.) 



H. rep ens. 



2. Rays of long birotulates few, (1 to 4) loilg, stout and claw-like ; 

 shafts with few spines ; rotul?e of smaller class very irregular ; 

 shafts abundantly spined. (PI. XI, fig. i and ii.) 



H. argj/rosperma. 



8. Rotulffi of long birotulates small ; rays hooked ; shafts spinifer- 



ous: rotulee of smaller class large, flat; margins lacinulate or 



delicately rayed ; shafts generally smooth. (PI. XI, fig. iv, v, 



and vi.) S. ryderu 



(1) Heteromeyenia repens, Potts. Proc. Acad. Nat. Sci. Phila. 1881, p. 150. (PI. 

 XI, fig. iii.) 



Spongilla repens, Potts. Proc. etc., 1880, p. 357. 



Sponge bright green, encrusting, thin. Texture loose and inco- 

 herent; the projecting lines of skeleton spicules giving it a pecul- 

 iarly rough appearance. 



Gemmulfe not very abundant, spherical ; with granular crust im- 

 bedding two classes of birotulate sj^icules as described. 



Skeleton spicules rather slender, subfusiform, sparsely micro- 

 spined ; gradually pointed. 



Dermal spicules fusiform, nearly straight, entirely spined ; spines 

 cylindrical, rounded ; those near the middle perpendicular, much 

 longer than the others. 



Gemniule-birotulates of the longer class comparatively few, stand- 

 ing amongst the others ; shafts smooth or microspined, nearly cylin- 

 drical, often irregularly bent. Rotulse dome-shajDed, the ends of 

 the recurved rays still further incurved like fish-hooks ; termina- 

 tions rounded. (PI. XI, fig. iii, b.b.) 



Birotulates of the shorter class very numerous and symmetrical, 

 about f the length of the others ; shafts generally largest near the 

 middle, or least near the rotules ; often with one or more conspic- 

 uous spines. Curvature of the rotules like that of a mushroom, or 

 rather flat umbrella ; rays not deeply notched ; rounded or slightly 

 incurved. (PL XI, fig. iii, c.c.c.) 



