316 A MONOGRAPH OF THE 



28. IsoDiCTYA OLAVA, Bowerbatik. 



Sponge. Massive, club-shaped, slightly pediceUed. Sur- 

 face hispid. Oscula simple, dispersed. Pores in- 

 conspicuous. Dermal membrane sparingly spiculoiis ; 

 spicula acerate, slender; as long as those of the 

 skeleton. Skeleton. DiiFusive ; primary lines rarely 

 more than bispiculous ; secondary lines unispiculous, 

 frequently two or three spicula wide ; spicula short 

 and rather stout. External defences, continuations 

 of the primary fasciculi. Interstitial membranes. 

 Tension spicula, acerate, slender, few in number. 



Colour. — Dried, light yellow, or fawn colour. 

 Habitat. — Moray Prith, the Rev. Walter Gregor. 

 Examined. — In the dried state. 



I am indebted to the Rev. Walter Gregor, of Macduff, 

 for my knowledge of this species. He obtained it from 

 the Moray Frith. There were two specimens, neither 

 quite five lines in height, on a rolled pebble, about two 

 inches in length, and nearly covered by Vermetus. Both 

 the specimens were club-shaped, with slightly expanded 

 bases. In the structure the skeleton somewhat re-t 

 sembles that of I. pallida, but the rete is more diflfuse, the 

 surface hispid, while that of /. pallida is smooth, and the 

 spicula of the two species very different in length ; those of 

 I. pallida being i^^th inch, while those of I. clava are jiySt inch 

 in length. The spicula of the skeletons of /. indistinda 

 and clava also resemble each other rather closely. They 

 agree in form and diameter, but the latter are less in 

 length than the former. The structural characters of these 

 two species resemble each other so closelyj that if it were 

 not for the well-defined difference in the external forms of 

 the sponge, they might readily be mistaken for each other. 



I could not, in the absence of the dermal membrane in 

 the specimens first described, detect the oscula, but in 



