92 Mr. n. J. Carter on the 



Bk., for me^ since, although I have taken my diagnosis from 

 Dr. Bowerbank's descriptions and illustrations [l. c), still, as 

 the skeletal spiculation of the former is almost precisely that 

 of the latter, which covered the twig on which the stato- 

 blasts alone of S. gregaria were found, to the extent of " five 

 inches," it seemed to be by no means impossible that the 

 spiculation of the two species might have been confounded. 

 Mr. Ridley's drawings are confirmatory of this possibility; and 

 thus the skeletal spiculation given by Dr. Bowerbank to 8. 

 gregaria becomes nearly identical with that of the foregoing 

 species, viz. S. Leidii, Bk. ; but while the ends of the spicules 

 are abrw^iXj pointed in the latter^ they are equally round in 

 8. reticulata and those stated by Dr. Bowerbank to charac- 

 terize the skeletal spicule of 8. gregaria. 



Undoubtedly we have the same sparsely spined skeleton- 

 spicule becoming smaller and thickly spined in the imme- 

 diate neighbourhood of the statoblasts in 8. Leidii, 8. gre- 

 garia, and 8. reticulata, together with absolutely smooth 

 skeleton-spicules in all three, if those assigned to 8. gregaria 

 by Dr. Bowerbank be the right ones. Thus the skeletal 

 spicules and the spicules of the statoblasts in 8. Leidii tending 

 to the characters of those assigned to 8. gregaria, in spite of 

 the roundness of the ends of the skeletal spicules in the latter, 

 seems to point out that the spinous element existed in both, 

 and that generally they are closely allied ; but, after all, it 

 does not satisfy our doubt as to whether the round-ended spicules 

 did not belong to 8. reticulata. Further observation is re- 

 quired to decide this. 



** Margin of disks denticulated. 



4. Meyenia Jluviatilis. 



Sponqillajluviatilis, Bk., No. 20, p. 7, pi. xxxviii. fig. 1 ; also No. 21, 

 vol. ii. p. 339 ; vol. i. pi. xxii. figs. 317-319 ; and No. 25, vol. iii. 

 pi. lix. 



Spongilla Jluviatilis auctt. 



Massive, lobat.e. Structure friable, crumbling. Colour light 

 yellow-brown. Skeleton-spicule curved, fusiform, gradually 

 sharp-pointed, smooth, often spined and often centrally inflated, 

 Statoblast globular ; aperture infundibular ; crust thick, 

 composed of the granular or microcell-substance, charged 

 with birotulates whose umbonate disks are deeply and irregu- 

 larly denticulated (PI. VI. fig. 11, a, h), arranged parallel to 

 each other and perpendicular to the chitinous coat. 



Loc. England and Europe generally. 



Ohs. Here, as elsewherej in proportion to the thickness of 

 the crust is the length of the infundibular aperture, which is 

 partly lined by a tubular extension of the chitinous coat. 



