348 Dr. B. B. EoU—On Fossil Sponges. 



fossilization, and is sometimes probably the cast of the outer surface 

 of the sarcode which has left its impress on the mould ; that it is 

 absent in the earlier and growing stages of the sponge, and is not 

 constantly present in the matured individuals of those species in 

 which it occurs ; and, moreover, that it sometimes results from the 

 contact of foreign bodies, in consequence of the increased density of 

 tissue which such bodies are apt to produce. Its value, therefore, 

 even as a specific character, is not great. 



Simple as De Fromentelle's arrangement may at first sight appear, 

 it is open to the objection that it is based upon characters that are 

 not always very constant or very well defined, and are liable to 

 graduate from one into another. Moreover it unites in one genus 

 or species individuals which, having a very close similarity in ex- 

 ternal appearance,, are totally different in the organization of the 

 skeleton, and, on the other hand, it separates others which, though 

 differing in outward characters, are closely allied in their structural 

 details ; for, however great may be the similarity in form or disposi- 

 tion of the oscules, etc., the power to secrete a framework composed 

 of spicula in one case, or entirely fibrous in another, appears to in- 

 dicate a difference in the nature of the sarcodal mass of higer 

 importance than mere outward configuration, which we know from 

 the study of recent species is frequently subject to considerable 

 variation, either from age, local peculiarities, or other circumstances. 

 Thus, Dr. Bowerbank, in illustration of the amount of variation 

 observable in the recent sponges, refers to our common British 

 Halichondria panieea, 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, 

 vnth an internal diameter of half or three-quarters of an inch. 

 When they attain such dimensions, their parieties are often of con- 

 siderable thickness, and their external surface becomes an inhalent 

 one, like the body of the sponge." ^ 



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

 appeared in the Transactions of the Linnsean Society of Normandy, 

 M. Etallon communicated to the Societe Jurassienne 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 regards the Clionidcs as 

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

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

 divides into two orders — 1st, the Dictyonocalidce or spicule-bearing 



1 I. c, p. 113. Here we have an example of an oscule passing into a cloaca as age 

 advanced, and an amorphous sponge becoming a fistulous one. 



