1887.] NATURAL SCIENCES OF PHILADELPHIA. 187 



recurved spiues, arranged tangentially, or centrifugally, like the 

 lines of a so-called "engine-turned" watch case." Carter, (Ann. 

 etc. 1881.) 



Syn. European: — See Vejdovsky "Diagnosis" under Euspon- 

 gilla laeustrisi p. 172, etc. 

 Syn. American: — 



1863 Spong ilia pauper cula, Bowerbank. 

 1863 " dawsoni " 



1875 " flexispina, Dawson. 



1879 " lacustrioides, Potts. 



1880 " abortiva, 

 1880 " mutica, 



1880 " montana, " 



1881 " multiforis, Carter. 

 1884 " lehighensis, Potts. 



As this is the most widely known of all the fresh water sponges, 

 and deserves a full and careful treatment, besides the analysis of it 

 given by Prof. Vejdovsky, under his name Euspotigilla lacustris, 

 I have also copied Mr. Cai-ter's description above, and now append 

 the result of my own observations, founded upon collections in all 

 parts of this country. 



As found in infinite numbers of situations and variety of forms in 

 North America, this sponge is green, when growing, as it does by 

 preference, in the light : from a sessile base freely and repeatedly 

 branching; branches cylindrical or more or less tapering; bristling 

 with the points of radiating spicules ; ends of the branches pointed 

 or rounded. Texture loose; the branching processes made up of 

 thick longitudinal lines of fasciculated spicules, united by single 

 spicules or more slender fascicles, in a radiating manner. Pores 

 numerous, large. 



Gemmules sub-spherical, often scarce until late in the year, 

 (November) when they are formed quite plentifully in the inter- 

 spicular spaces, not only in the sessile portion, but throughout the 

 branches of the sponge. Granular crust of the gemmules very 

 variable in thickness ; in some forms altogether wanting. Foraminal 

 aperture infundibular. 



Skeleton spicules curved, fusiform, gradually sharp pointed, al- 

 most uniformly smooth. 



Dermal or flesh spicules variable in number, but genei-ally very 

 numerous ; curved, fusiform, gradually tapering to sharp points ; 

 densely and entirely spined. 



