1873.] DR. J. S. BOWERBANK ON THE SPONGIADjE. 32" 



regularity does not extend beyond the length of the shafts of the 

 connecting-spicula ; all beneath that point to the centre of the 

 sponge is entirely devoid of regularity. The intermarginal spaces 

 and the interstitial membranes within them are crowded with the 

 stellate retentive spicula ; but below the terminations of the retentive 

 spicula they were comparatively few in number, and in the inner and 

 central parts of the sponge they are rarely, if ever, to be found. 

 The retentive stellate spicula are of two descriptions. The attenuato- 

 stellate ones are small and nearly uniform in size, a few large ones 

 occasionally appearing among them. The cylindro-stellate ones are 

 very minute, not exceeding one third or one fourth the diameter of 

 the average-sized attenuato-stellate ones. 



I did not succeed in finding the slender porrecto-ternate or 

 recurvo-ternate spicula in situ ; but a few fragments of each were 

 found among the spicula obtained by the aid of nitric acid. By the 

 same means also I detected the presence in the sponge of a few 

 deltoid spicula. 



Pachymatisma contorta, Bowerbank. (Plate XXXI.) 



Sponge branching ; branches irregular, short, stout, anastomosing; 

 surface undulating. Oscula simple, dispersed, small. Pores incon- 

 spicuous. Skeleton-spicula acerate, large and long, and occasion- 

 ally acuate, large and long. Connecting-spicula attenuato-patento- 

 ternate, rare and very variable in size. Interstitial membranes — 

 tension-spicula acerate, short and stout ; retentive spicula attenuato- 

 stellate, comparatively large, and attenuato-sphero-stellate, minute ; 

 radii more or less acutely conical. Ovaria obtusely oval, slightly 

 depressed, component cuneiform spicula small and slender. 



Colour, in the dried state, light brown. 



Hab. Fiji Islands (-Sir Everard Home). See Catalogue of Pori- 

 fera in the Museum of the Royal College of Surgeons, part i. 18G0, 

 p. 126, B. 166. 



The short branches of this sponge vary in diameter from 3 to 9 

 lines, and in the greater part of the sponge are so much anastomosed 

 as to almost form an irregular mass. The surface is somewhat 

 uneven and undulating ; and in some of the most protected parts 

 there are a few spicula that project from between the ovaria ; but the 

 specimen has so many fragments of parasitical sponges attached to 

 it as to render the slight proofs of its hispid character doubtful. 

 The oscula are few in number, and the largest was scarcely a line in 

 diameter. I could not determine the characters of the pores, in 

 consequence of the destruction of the dermal membrane by weather- 

 ing or washing. The dermal crust of the sponge is hard and very 

 compact, and in some parts attains a thickuess of nearly a line. 

 The radiating structure immediately beneath the dermal crust, so 

 striking and characteristic in the greater number of the species of 

 this genus, is in this species almost obsolete ; and the irregular 

 central portion of the interstitial tissues extends in many places quite 

 to the inner surface of the dermal crust ; while in other parts the 



