304 A MONOGRAPH OF THE 



20. IsouiCTTA ROBBSTA, Bowerbunk. 



Sponge. Cup or fan-shaped, pedicel ? short. Surface ; outer 

 or inhalant one smooth; inner or exhalent one, fur- 

 nished with numerous large oscula. Oscula dis- 

 persed, simple, or slightly elevated. Pores incon- 

 spicuous. Dermal membrane pellucid, abundantly 

 spiculous ; spicula dispersed, acerate, same as those 

 of the skeleton. Skeleton. Primary lines frequently 

 large and numerously spiculous ; secondary lines very 

 irregular, often multispiculous ; spicula acerate, very 

 rarely acuate, large and strong. Interstitial mem- 

 branes. Retentive spicula simple bihamate, nearly 

 semi-circular, minute, and very few in number. 



Colour. — Dried, light ochreous yellow. 

 Habitat. — Shetland, seventy to ninety fathoms, Rev. 

 A. M. Norman. 



Examined. — In the dried state. 



I received this species from the Rev. A. M. Norman, 

 who dredged it at Shetland in 1861. The sponge is ir- 

 regularly cup-shaped, about an inch and a half in height, 

 and three and a quarter inches wide at its greatest expan- 

 sion. Its thickness varies from two to' about five lines. 

 It has every appearance of having at an early period of its 

 growth been attached to some base by probably a short 

 pedicel, but there are no remains visible of such an attach- 

 ment at the present time. The oscula are numerous and 

 large, frequently attaining a diameter of two lines, and an 

 elevation of about a line. The skeleton has singular 

 structural peculiarities. What we should designate the 

 primary and secondary lines of the skeleton, considering it 

 as an Isodictya, are in perfect accordance with the usual 

 forms assumed in the corresponding parts in the best 

 developed specimens of that genus ; but in addition to 

 these structures, there are large multispiculous fasciculi, 



