1873.] DR. J. S. BOWERBANK ON THE SPONGIAD^. 13 



The remarkable forms of these spicula, combined with the inequi- 

 cylindrical skeleton ones, render the discrimination of this species 

 comparatively easy. 



The ovaria in the dermal crust are all fully developed ; but on the 

 interstitial membranes they may be seen in all stages of develop- 

 ment, from a size not exceeding that of one of the largest of the 

 stellate spicula to that of the fully developed ovarium. 



Geodia media, Bowerbank. (Plate II.) 



Sponge massive, sessile ; surface smooth. Oscula congregated in 

 slightly depressed areas. Pores inconspicuous, congregated. Der- 

 mal membrane obsolete. Sheleton-fasciculi large, multispiculous, 

 rather closely compacted ; spicula fusiformi-acerate, short and stout. 

 Connecting spicula attenuato-patenti-ternate, rather short, strongly 

 developed. Interstitial membranes — tension-spicula acerate, small 

 and few ; retentive spicula attenuato-stellate, radii acutely conical, 

 very variable in number, and cylindro-stellate very minute. Ovaries 

 slightly oval, depressed. 



Colour in the dried state pale buff-yellow. 

 Hab. Mexico {Mr. Thomas Tng all). 

 Examined in the dried state. 



I received this sponge from my late friend Mr. Thomas Ingall, 

 labelled Mexico. The reverse side to that figured is smooth and re- 

 gularly curved, with faint parallel striae at right angles to the curve, 

 as if it had been based on a shell with raised lines upon it or on the 

 stem of a coral. The mass of the sponge is not perfect, portions 

 having been broken away from both ends of it ; but the specimen has 

 evidently never been much larger than it is at present. The oscula 

 occupy two well-defined areas, which are very slightly depressed. 

 The porous areas are visible by the aid of a lens of two inches focus ; 

 they are not so numerous as in many other species of this genus. I 

 could not find any remains of the dermal membrane. The skeleton 

 is rather strongly constructed ; the skeleton-fasciculi are both large 

 and numerous. The connecting spicula are also strong and numerous ; 

 and their shafts, incorporated with the distal ends of the skeleton- 

 fasciculi, contribute greatly to the strength and firmness of the skele- 

 ton-structures immediately beneath the dermal crust. In their adult 

 state the connecting spicula are large and strong, and their radii pa- 

 tenti-ternate ; but in the young and immature condition they are 

 more or less expando-ternate, and they are found in every stage of 

 development. There were very slight indications of the presence of 

 recurvo-spicula. I observed among the spicula separated by nitric 

 acid the remains of one very small specimen, and a fragment of 

 another in one of the sections mounted in Canada balsam. 



The tension-spicula of the interstitial membranes are very small 

 and few in number. 



The largest description of attenuato-stellate retentive spicula vary 

 to some extent in the number of their radii ; some have but three or 

 four, while others have as manv as twelve or fourteen. In the 



