1887,] NATURAL SCIENCES OF PHILADELPHIA. 221 



M. fluviatilis certainly cannot be called a branching sponge, but 

 in some localities, particularly when growing on the lower side of 

 timbers etc. or in a rapid current, I have found it bearing incon- 

 sequent processes about an inch in length. In color it inclines to a 

 light brown or yellowish, but in our clear northern lakes, where it 

 grows in large patches exposed upon the upper surface of stones, it 

 is described as of a vivid green. 



Meyenia fluviatilis, var. meyeni. 



Spongilla meyeni, Carter. 



Skeleton spicules sparsely microspined, long, cylindrical. Gem- 

 mules spherical; chitiuous coat and granular crust relatively thick. 

 Birotulates often in two or three partial series ; shafts long, cylin- 

 drical, generally smooth ; rays of the rotules long, conical, deeply 

 divided. An occasional spicule may be found of an intermediate 

 character betAveen the acerates and the birotulates ; — that is, it 

 resembles a short acerate with whorls of short spines about one 

 fourth its length from either end. 



In his Monograph of 1881 Mr. Carter dropped this one of his 

 original species of Bombay sponges from his classification, merging 

 it with M. fluviatilis. For several reasons I incline to retain it as a 

 variety of that species. The size of the birotulates is far greater 

 than the average in the tyjiical species, and their cylindrical shafts 

 and symmetrical forms give them a peculiar beauty. Their occa- 

 sional arrangement in multiple series is not luiique, but the habit 

 was first noticed in this variety. 



Meas. Skeleton spicules 0-0108 by 0-0004 i.iches. Length of 

 average birotulate O'OOIS inches. Diameter of rotule 0*001 inches. 



M. fluviatilis, form astrosperma, Potts. Syn. Proc. Acad. etc. 

 1880, p. 357. 



The name "star seeded" was applied before the author had the 

 opportunity to compare this with the European type, or even 

 with collections from other parts of this country. It is a beautiful 

 form of the species, with birotulates suflliciently scattered over the 

 surface of the gemmule, to show as stars u|)on a silver dome (PI. V. 

 fig. V.) It was found at Lehigh Gap, Pennsylvania ; but cannot 

 claim to be even a variety. 



M. pohjmorpha, Syn. was suggested to me by the great numbers 

 of misshapen or incomplete forms surrounding the statoblasts ; as in 

 (PI. IX, fig. iv, e, e, e.) These, as my friend Mr. Carter has shown 

 me, are nearly all abortive birotulates; and when we inquire into 

 their cause we find that they occur almost solely upon gemmules 



