222 PROCEEDINGS OF THE ACADEMY OF [1887. 



where the granular crust is wanting. How this absence so affects 

 them, and, in fact, how this chxss of sj^icules is developed upon the 

 chitinous coat, must be left to the investigations of later students. 



The abnormal habit just mentioned leads us to consider the next 

 variety, in which the modification assumes greater definiteness. 



M. fluviatilis v;u-. acuminata, Potts. (PI. IX, fig. ii.) Proc. Acad. Nat. Sci. 1S82, 

 p. 70. 



"Sponge j^robably altogether sessile and massive, consisting of an 

 intertexture of stout, fusiform-acerate skeleton spicules, abruptly 

 pointed, coarsely spined, excejDt near the extremities; spines sub- 

 conical, acute, dermal spicules absent or undiscovei'ed. Gemmules 

 without granular crust; some of them supporting a few, misplaced, 

 irregular or malformed birotulate spicules, the distinguishing feature 

 of which, is the prolongation of the familiar boss or umbo upon the 

 outer surface of each rotule, into a long, acuminate spine, in line 

 with and a continuation of the shaft." 



Meas. Skeleton spicules 0"00985 by 0"0005 inches. Length of 

 birotulates 0*00107 inches. Diameter of rotules 0'0007 inches. 



To the description above quoted from the "Proceedings etc.," is 

 appended the following in regard to the association of this variety 

 of M. fluviatilis with Spongilla yar. pauper^cula in the Boston Water 

 supply. 



"The exceptional features referred to as marking this collection 

 of sponges, were ; first, the fact that all the gemmules, whether be- 

 longing to the genus Spongilla or Meijenia, were smooth, that is 

 without a granular or cellular crust ; second, the apparent absence 

 of dermal spicules from both, and the abnormal character of those 

 belonging to the gemmules. The occurrence of naked gemmules is 

 not infrequent, but has, so far as known, heretofore been limited to 

 the genus Spongilla. The discovery of the same feature in the 

 associated genus Meyenia, coupled with the fact that of the small 

 number of birotulates found upon them, a large proportion were 

 imperfect, the rays being more or less aborted, approximating their 

 shape to that of the sjjined, fusiform acerates of Spongilla, gave rise 

 to the suggestion that here, possibly, had been not merely a mechan- 

 ical mixture, by inter-, or super-position of two dissimilar species, 

 but an organic hybridization, produced by the flowing together of 

 the amoeboid particles of which the sponge flesh is composed." 



Meyenia fluviatilis, var. mexicana, Potts. Am. Nat. Aug. 1885, p. 810. 



I find little of novelty in my description of this variety except 

 the following. "Birotulate spicules pertaining to the gemmules, in 



