168 BEITISH SPONGIAD^. 



resemble both in size and form those of R. intermedium, 

 but R. simplicissimumis entirely destitute of bihamate, 

 retentive spicula, and in the dermis the spicula are 

 very numerous and are irregtilarly dispersed, and in 

 no degree approaching reticulation. The loosely 

 fasciculated dermal spicula and numerous rosette- 

 shaped groups of retentive, inequi-anchorate spicula in 

 the dermis of R. sordidum readily separate it from 

 R. intermedium. In truth the sponge in course of 

 description is really an intermediate species between 

 R. simplicissimum and R. sordidum. 



" It is quite possible, though not very probable, from 

 the rarity of the inequi-anchorate spicula in R. infcr- 

 medium that hereafter a few rosette-shaped groups may 

 be found in well-developed specimens of the species ; 

 as we find in R. sordidum they do not occur equally in 

 all parts of the dermal membrane, and in some por- 

 tions of it they are entirely absent." 



Genus 24. SPONGILLA, Linn., i, 199 ; n, 10. 



1. SPONGILLA FLUVIATILIS (Pallas), n, 339; i, PI. IX, 

 figs. 217, 218; PL XXII, figs. 517519; in, 

 PI. LIX. 



1867 Ephydatia fluviatilis, Gray. Proc. Zool. Soc., p. 550. . 



2. SPONGILLA PAEPITTT, Carter, in, 298, PL LXXXVI, 

 figs. 512. 



1S6S Spongilla Mayeni, var. Parfitti, Parfitt. Sponges of 

 Devonshire, Trans. Devon. Assoc. Liter. Sci. and Art, 

 p. 17 (separate copy). 



