1872.] DR. J. S. BOWERBANK ON THE SPONGIAD/E. (32!) 



imbedded. The specimen from Jamaica is rather larger than the 

 type one ; it is 8^ inches in length by 4^ inches in breadth. The 

 two specimens are very similar in all their external characters ; there 

 is only this difference in their condition — that while in the type 

 specimen nearly all the oscula in the sunken areas on the tumuloid 

 bodies are open, in the specimen from Jamaica the greater number 

 of them are closed, and it is only in two or three of the smaller 

 groups that they are open, and exhibit precisely the same characters 

 as those in the Honduras specimen. Both specimens are more or 

 less covered with thin light-brown parasitical Isodictyas, and espe- 

 cially on their under surfaces. There are none of the oscular areas 

 on the underside of either of the two specimens ; nor could I detect 

 a single osculum on any other part of the specimens than those 

 within their proper boundaries. The porous areas are visible to the 

 unassisted eye ; they are very numerous, and closely adjoining each 

 other. In a thin slice from the dermal surface, mounted in Canada 

 balsam and viewed with a power of 180 linear, they were very di- 

 stinctly exhibited. Each porous area was furnished with a thin and 

 very pellucid membrane, on which was dispersed an innumerable 

 quantity of exceedingly minute cylindro-subsphero-stellate spicula, 

 and a few very slender acerate tension ones. The pores in the 

 greater number of the areas were closed ; in a few they were open, 

 and in these their number did not exceed four or five ; when in a 

 closed condition their positions were frequently indicated by minute 

 circular areas destitute of the surrounding minute stellate spicula. 



The dermal crust of the sponge is very thick ; it is composed of 

 an infinite number of fully developed ovarian bodies closely packed 

 together. The whole of them appeared of uniform density. The 

 external dermal membrane was crowded with closely packed very 

 minute attenuato-stellate spicula, with a few small acerate tension 

 ones. 



The ternate apices of the fully developed connecting spicula are 

 cemented firmly to the inner surface of the dermal crust ; and their 

 shafts descend amidst the distal ends of the skeleton-fasciculi. The 

 greater number are purely ternate ; but occasionally one or more of 

 their radii become furcated. At a short distance beneath the crus- 

 taceous dermis, imbedded amidst the skeleton-fasciculi, a few young 

 ternate spicula may frequently be seen in an incomplete state of 

 development, as if in reserve, to be brought forward if necessary for 

 the support of the crustaceous dermis. 



The skeleton-fasciculi are rather irregularly disposed, but they 

 always, more or less directly, radiate in lines from the centre of the 

 sponge, or of the projecting parts of it, to the surface. The inter- 

 stitial membranes are furnished with the same description of small 

 acerate tension-spicula that are found in the dermal membrane, and, 

 as in that organ, they are few in number. The retentive spicual are 

 different from the very minute ones that abound in the dermal mem- 

 brane. They are the same description of spiculum, but very much 

 larger, and have much fewer radii, and they are very long and acute. 

 The interstitial membranes abound also with ovarian bodies in all 



