GRANTIA. 173 



was actuatied in making his alteration by regard to a canon 

 which some have laid down, — that generic names commemo- 

 rative of naturalists ought to be confined to botany ; but since 

 there appears no sufficient reason for such a restriction, and 

 since the canon has been too frequently violated to be now kept 

 in integrity, e. g. Cuvieria : Mulleria : Montagua : Cavolina : 

 Skenia : Leacia : Elfortia : Rissoa : Peronia, &c. See. I willingly 

 here adopt the original name of the genus, the more so as the la- 

 bovirs of Dr Grant in various departments of zoology, and more 

 especially as a professor of the science in the University Col- 

 lege of London, claim for him the highest recompense which 

 the cultivators of the same field have to bestow. 



The essential character of the genus is the existence of spi- 

 cula of carbonate of lime in the texture of the sponge, and the 

 fact is readily ascertained by the efiervescence which ensues on 

 its immersion into a dilute acid. These spicula are crystalline, 

 exceedingly numerous, partly triradiate and partly imdivided, 

 — the triradiate chiefly bounding the pores and orifices, while 

 the curved ends of the others hang over the exterior entrances 

 of the pores to protect them. When they are all entirely re- 

 moved by the aid of an acid, the sponge becomes very soft and 

 flexible, but still retains its original form and appeai'ance ; and 

 if now examined with a microscope the residuum will be found 

 a gelatinous membrane apparently of vuiiform and homogeneous 

 composition throughout, without any pores or interstices, but 

 with the cavities on the inner surface the same as in the per- 

 fect sponge. The Grantiai differ, therefore, from most other 

 sponges in their base not being fibrous, and in their pores being 

 rather of the nature of perforations than of meshes left by the 

 interlacing of threads. From the number of their spicula, and 

 their calcareous quality, it happens also that the Grantia) are 

 more compact and close in texture than other sponges, and of a 



