54 J. G. WALLER ON VARIATION 



of S. jluviatilis, yet it differs from that which is described by Dr. 

 Bowerbank, as typical of the species, in some minute particulars, to 

 which I shall particularly direct your attention. 



The specimen described as the typical Spongilla Jluviatilis, was 

 found in the West Country Timber Dock, at Rotherhithe, and its 

 characters are thus tabulated : — 



Sponge massive, sessile ; surface uneven, often lobular, hispid. 

 Oscula simple, large, scattered. Pores conspicuous ; dermal mem- 

 brane pellucid, aspiculous. Skeleton ; spicula acerate ; ovaria sub- 

 globose ; spicula birotulate, short, rarely spinous ; disposed in lines 

 radiating from the centre of the ovarium ; rotula equal in size, 

 flat, deeply and irregularly dentate, diameter equal to the length of 

 the shaft of the spiculum. 



Now the difference between this description and of that of the 

 river Exe, is, that the skeleton spicules of the latter are of two 

 kinds — one smooth as before, the other " incipiently spinous " — 

 both irregularly mixed in the skeleton, but the latter fewer in num- 

 ber. The spicules of the ovaria are, more or less, spinous ; spines 

 long and acutely terminated. Mr. Parfitt, in a letter to Dr. 

 Bowerbank, stated that he considered the species as intermediate 

 between S. Jluviatilis and S. Meyeni of the Bombay tanks. Mr. 

 Carter, descrit ing it in the "Annals and Mag. Nat. Hist." April, 

 1868, calls it S. Meyeni, var. Parfitti. His description is fuller 

 than that of Dr. Bowerbank, and I shall refer to it again. 

 He appends the following observations : " This Spongilla 

 chiefly differs from Sp. Meyeni, of Bombay, in the decidedly spinous 

 character of one-third of its largest spicules, while about the same 

 proportion in the Bombay species can only be termed ' incipiently 

 spinous.' The excess of size of the elementary parts generally of 

 the Bombay species over those of the variety in the river Exe 

 amounts to nothing specifically considered." 



" But there is a much more decided difference between var. 

 Parfitti and the birotulate English species Sp. Jluviatilis, which 

 also grows in the river Exe, inasmuch as the spicules of the skeleton 

 of the latter are all smooth, the shaft of the birotules somewhat 

 constricted in the centre, approaching to the hour-glass shape, with 

 the margin only of the rotules minutely dentate, almost fringed." 



Now, it is necessary to observe, that the claim of the Spongilla of 

 the Exe to be a new species allied to that of S. Meyeni is pointed 

 out to be the spinous condition of a portion of its spicules, but it is 



