180 Mr. H. J. Carter on Meyenia fluviatilis. 



several handsome specimens for distribution among the 

 museums in this country, and proposes to send more ; hence 

 I have already been able to enrich the collections of Spongillce. in 

 the British and Liverpool Museums respectively to this extent. 

 Not confining his researches to the Niagara River, Mr. 

 Mills has also not forgotten the subject when abroad, although 

 engaged in other matters probably of more importance, so 

 that during his last two visits to Florida he has been almost 

 equally successful there in his discovery of the freshwater 

 sponges, and equally generous in sending about specimens of 

 them on his return to Butfalo. One of them, which he has 

 kindly sent to me, he has, at my suggestion, designated a 

 variety of Meyenia fluviatilis^ under tlie name of ^^ gracilis ^^ 

 and this, from his accompanying data, together with two 

 slides and a bit of the sponge itself in spirit, I shall, at 

 his request, presently describe for publication ; the rest, in- 

 cluding his Meyenia Everetti, from Massachusetts, will 

 probably appear in Mr. Potts's forthcoming Monograph of 

 the freshwater sponges of North America. 



Meyenia fluviatilis^ var. gracilis. 



Delicate in structure, which is soft, whitish or colourless in 

 spirit, presenting the aspect of glue or sarcode when dry ; 

 growing over the stem of an aquatic plant in a thin layer 

 charged beneatli with statoblasts (gemmules). Spicules of 

 two forms, viz. : — 1, skeletal, very fine and delicate, acerate, 

 curved, cylindrical, about 34 to 36 by ^-GOOOth inch in its 

 greatest dimensions, chiefly confined to the fibre ; 2, stato- 

 blast-spicule, shaft long, cylindrical, often slightly curved, 

 smooth, also very thin and delicate; head small, flat, radiately 

 denticulated, the ends of the rays not recurved; often 

 umbonated by a projecting spine or process, total length 

 about 7-6000ths inch, head H-6000ths inch in diameter, 

 shaft about five times longer than the diameter of the head, 

 about :^-6000th inch thick ; chiefly confined to the statoblast, 

 but also loose and numerous in the tissue generally. Stato- 

 blast globular when wet, hemispherical and depressed in the 

 direction of the aperture when dry ; when fully formed about 

 65 to 75-6000ths inch in diameter. Aperture slightly mar- 

 ginatedj i. e. slightly raised above the common level, about 

 8-6000ths inch in diameter. Surface of statoblast rough or 

 uneven. In a section through the centre the crust is seen to 

 be a little thicker than the length of the birotules, which, as 

 usual, are arranged perpendicularly to the yellow chitinous 

 coat beneath and parallel to each other, with one head resting 



