202 PROCEEDINGS OF THE ACADEMY OF [1887. 



Spongilla fragilis, (S. segregata, Potts.) Syn. 



My error in separating this form has been acknowledged. 



S. fragilis, (S. calumeti, Thomas.) Syn. 



This form has very robust gemmule spicules. (PI. VIII, fig. iii.) 



S. fragilis, var. minuta, Potts. (PI. VIII, fig. iv.) Proc. Acad. Nat. Sei. 1880 

 p. 357. 



This varietal name was given to a sponge first found at Lehigh 

 Gap, Pennsylvania, in which the gemmules were much smaller than 

 in the typical form, while the surrounding spicules were nearly 

 double the length of those of the same class in it and were nearly 

 always terminated by a single sharp spine. It has since been found 

 at several other localities. 



Meas. Skeleton spicules 0.01 by 0.0004 inches. Gemmule spic- 

 ules 0.00463 by 0.00025 inches. 



S. fragilis, var. minutissima, Potts. (PI. VIII, fig. ii.) 



The gemmules of var. minutissima are still smaller than those of 

 var. minuta ; the groups consist of greater numbers of individuals ; 

 the cell-structure surrounding them is still coarser and more conspic- 

 uous. The skeleton spicules of those collected in Lake Hopatcong, 

 New Jersey, (alt. 1200 ft. above tide.) are very slender and although 

 gathered in October often centrally inflated. 



Meas. Skeleton spicules 0. 0064 by 0.00015 inches ; gemmule do. 

 0.00397 by 0.0001 inches. 



S. fragilis, v. irregularis, Potts. 



In this, which was also collected at Lake Hopatcong, the skele- 

 ton spicules are short and slender ; gemmule spicules irregularly 

 bent and inflated. 



Meas. Length of skeleton spicules 0.0042 inches ; of genunule 

 do. 0.003 inches. 

 (14) Spongilla igloviformis. Potts, n. sp. (PI. V, fig. iii. PI. VIII, fig. v.) 



Sponge light or dark brown, encrusting, thin ; surface somewhat 

 corrugated, or smooth, excepting the projecting points of spicules. 

 Lines of skeleton spicules much dispersed, forming no recognizable 

 intertexture ; the sarcode in this species being at its maximum, in 

 relation to the skeleton spicules, which are seen at their minimum 

 as to numbers. 



Gemmules very numerous, in compact groups of eight or ten to 

 twenty or more; irregularly disposed upon, but not attached to, the 



