PLATE LXXVIII. 243 



number can rarely be determined, while the areas are 

 large and irregular, thus producing a striking and very 

 characteristic specific difference between the two 

 sponges. The arrangements of the skeleton structures 

 of the two species would scarcely distinguish them, 

 although those of I. Ing alii appear to be much more 

 regular than those of I. simulans. 



DESMACIDON COLUMELLA, Bowerlan/c. 

 Plate LXXVIII. 



Sponge. Massive, ascending, compressed. Surface 

 smooth, uneven, with deep furrows. Oscula terminal ? 

 Pores inconspicuous. Dermal membrane spiculous ; 

 spicula dispersed or subfasciculated, same form and 

 size as those of the skeleton. Skeleton : fibres stout, 

 and compact, rete coarse and open, spicula fusiformi- 

 cylindrical, long, and rather slender. Interstitial 

 membranes spiculous. Spicula same as those of the 

 skeleton, rather abundantly dispersed. Gemmules 

 membranous, aspiculous, large, and pellucid at their 

 margins, with a central nucleus more or less distinct. 



Colour. White, with dark orange longitudinal veins 

 when alive. Light brown in the dried state. 



Habitat. Exmouth, in tidal pools ; Mr. Edward 

 Parfitt. 



Examined. In the dried state. 



I am indebted to Mr. Edward Parfitt, of Exeter, for 

 my knowledge of this interesting species of sponge. 

 In form it is a slightly curved compressed column, 

 decreasing in breadth from near the base to its apex. 

 The half of the specimen kindly presented to me by 

 Mr. Parfitt is fourteen lines high, and six lines at its 

 greatest breadth near the base. Mr. Parfitt states in 

 the letter which accompanied the specimen that it was 

 "found at Exmouth in tidal pools, but very rare. 

 When alive it was like an Ascidian, for which I took it 

 when seen growing. Colour nearly white, with two or 



