EXPLANATION OF THE PLATES. 259 



PI, ATE XVI. Fig. 1, Halichondria hirsuta of the natiJral size. 

 F"ig. 2, Hal. mammillaris of the natural size, from a specimen in 

 the collection of William Thompson, Esq. Fig, 3, Hal. sevosa, 

 natural size. Fig. 4, A portion magnified to show the spicula protrud- 

 ing from the organic mucus. Fig. 4, b. The spicula highly magnified. 

 Fig. 5, Alcvonidiuji gelatinosum in its primary state. The 

 figure was engraved before the real nature of the production was de- 

 tected. Fig. 6. Dysidea PAPILL0S4 of the natural size, and Fig. 

 7, one of the papillae slightly magnified, with a section of the same. 

 P'ig. 8, Haltsarca Dujardinii, natural size. 

 PLATE XVII. Spongilla fluviatihs. Fig. 1, in its crustaceous, 

 and Fig. 2, in its massive state. Fig. .3, represents it throwing up 

 branches from a crustaceous base. 

 PLATE XVIII. Spongilla fluviatilis, in its arborescent state, with 



its spicula and seminiferous capsules. 

 PLATE XIX. Fig. 1, Spongia pulchella, from a fine specimen in 

 the collection of the late Mr Templeton. P'ig. 2, The same from a 

 specimen found in Berwick bay. Fig. 3, 4, 5, Spongia limbata, 

 from specimens from very remote localities. 

 PLATE XX. Fig. 1, Grantia compressa, of the natural size, from 

 specimens gathered in Berwick bay. Fig. 2, Gr. laccnosa of the 

 natural bize, and fig. 3, the same magnified, from a specimen sent me 

 by JMr W. Bean. Fig. 4, Ga. ciliata, from a drawing made from 

 the living sponge by JMr Edward Forbes. Fig. 6, Grantia nivea, 

 a state of, from the coast of Ireland. Fig. 7, Gr. fistulosa, from 

 a small specimen sent to me by .VIr William Thompson. Fig. JJ, 8, 

 Halcchondria albescens, of the natural size, with iis spicula. 

 PLATE XXI. Fig. 1, 2, Grantia botryoides, as very commonly met 

 with. Fig. 3, Gr. botryoides in an abnormal state from growing 

 underneath a flat stone. Fig. 4, A portion of this Grantia as seen 

 through a magnifier. Fig. 5, A minute portion of the surface more 

 highly magnified. Fig. C, Specimens of Grantia ciliata in an 

 unusual state or form; and Fig. T, one of the same seen through a 

 magnifier. Fig. 8, Gr. nivea of the natural size. Fig. 9, Gr. co- 

 riacea, natural bize. 

 PLATE XXII. Fig. 1, Corallina officinalis in its crustaceous and 

 lichenoid state. Fig. 2, CoR. officinalis, when full grown and in 

 its normal form. Fig. 3, 4, 5, A small portion, from different speci- 

 mens, magnified ; Fig. 3 was drawn after the calcareous crust had been 

 removed by an acid, l-'ig. C, A small portion of Fig. 2, deprived of its 

 calcareous matter and highly magnified. Fig. 7i The seniinul granules, 

 copied from Ellis. Fig. 8, A portion of the Nullipora agarici- 

 formis deprived of its calcareous earth, and highly magnified, to show 

 its structure. 



