Harvey B. Hall— On Fotis'd Sponges. '77 



the other hand, it separates others, wliich, though differing in out\vard 

 characters, are closely allied in their structural details ; for, however 

 great may be the similarity in form or disposition of the oscules, etc., 

 the power to secrete a framework composed of spicula in one case, or 

 entirely fibi'ous in another, ajipears to indicate a difference in the nature 

 of the sarcodal mass of higher importance than mere outward con- 

 figuration, wliich we know^ from the study of i-ecent species is 

 frequently subject to considerable variation, either from age, local 

 peculiarities, or other circumstances. Thus Dr. Bowerbank, in illus- 

 tration of the amount of variation observable in recent sponges, refers 

 to our common British Halichondria panicea, which, when of small size, 

 has the oscules " situated on the surface of the sponge, and are scarcely, 

 if at all, elevated above the dermal surface ; while in large specimens 

 of the same species we find them collected in the inside of elongated 

 tubular projections or common cloaca, which vary from a few lines only 

 in height and diameter to tubular projections several inches in height, 

 with an internal diameter of half or three quarters of an inch. When 

 they attain such dimensions, their parieties are often of considerable 

 thickness and their external surfiice becomes an inhalent one, like the 

 body of the sponge." [Here we have an example of an oscule passing 

 into a cloaca as age advanced, and an amorphous sponge becoming a 

 fistulous one.] 



IV. About the same time that "M. de Fromentelle's Memoir 

 appeared in the Transactions of the Linmean Society of Normandy, 

 M. Etallon communicated to the Society Jurassiene some papers on the 

 sponges of the Upper Jurassic rocks, in which he proposed a new- 

 arrangement of the species and genera, based on the structural details 

 of the skeleton. As he treats only on those fossil sponges which belong 

 to the Upper Jura, his classification is necessarily incomplete ; but it 

 is, nevertheless, sufficiently so to foreshadow his views on the subject 

 generally. Like D'Orbigny, he regarded the Clionlda as horny 

 sponges, and forms them into an order by themselves ; while the 

 testaceous sponges, included in the Petrosponrjldce of M. Pictet, he 

 divides into orders — 1st, the Did)/onoc(dida' or spicule-bearing sponges, 

 and 2d, the Spongutires vermicales, or ti'ue Fetroi^pong'uhK. [The 

 CUonida' are, however, only the accidental occupants of the cavities 

 in which they are found, having located themselves in the excavations 

 formed by Annelida? and the terebrating mollusks. For the most part 

 they are spicular sponges.] 



With respect to the first of these groups, M. Etallon observes : 

 " There are among the testaceous sponges, which do not enter into 

 the family of Petrospongidce , some that have their skeleton made up of 



