Dr. B, B. mil— On Fossil Sponges. 343 



not described as having any red tint. It does not colour the fields 

 red, when free from drift, but pale yellow fragments lie thick upon 

 the soil. The marls above form red soil, and the upper limestone 

 which " contains little or no magnesia " " has often a red tint." If 

 both these beds contain iron in the same form, why is the upper one 

 peroxidized and the lower one not so ? Were Mr. Ward's expla- 

 nation the true one, the lower limestone ought certainly, at least 

 here and there, to be reddish ; but, as before stated, neither this bed, 

 nor the grits on which it is seen to rest in clean section, are at all 

 red, where I have seen them, except in the one case where a bed 

 of red marl lay between the grit and limestone. 



III. — Notes on Fossil Sponges. 

 By Harvey B. Holl, M.D., F.G.S. 



(PART II.) 



{Continued from page 315.) 



III. Pictet converted D'Orbigny's families into tribes, and intro- 

 duced some additional genera created by Giebel, King, etc. ; and, 

 except in the description of new genera and species by Eeuss, 

 Koemer, Salter, Eichwald and others, the subject remained very 

 much where D'Orbigny left it until M. de Fromentelle proposed a 

 new arrangement, based upon what he terms the " organs which 

 serve for the nutrition of the sponge," — viz., the tubule, oscules, 

 pores, etc. Like D'Orbigny, he divides the sponges into two orders : 

 n st, the Spongiaria, which comprises only recent genera ; and, 2nd, 

 the Spongitaria, which contains all the fossil genera, with the excep- 

 tion of the doubtful group, the ClionidES. The second order is 

 further divided into three sub-orders : 1, those sponges which have 

 one or more tubules (the Spongitaria tubulosa) ; 2, those that have 

 oscules, but no tubule {Spongitaria osculata) ; and 3, those that have 

 neither tubule nor oscules {Spongitaria porosa). Each of these sub- 

 orders is further divided thus : the tubular sponges into those in 

 which the tubule is solitary, and those in which it is grouped, and 

 also into those with oscules and those without oscules. The oscular 

 sponges are similarly subdivided, according to form, disposition of 

 the oscules, and presence or absence of an epitheca. Lastly, the 

 porous sponges are divided into those that are more or. less regularly 

 cup-shaped, and those that assume some other form. 



In this arrangement no importance is attached to the nature of the 

 sponge-tissue as a character. In fact, M. de Fromentelle states that 

 he considers it to have " a value altogether secondary, for it is not 

 the form or composition of the skeleton which determines the 

 functions, but the functions themselves which give to the 

 animal the particular form which characterizes it." ^ It is not 

 necessary, however, here to discuss this question, further than to 

 observe, that the power which the sponge has to secrete a siliceous 

 spicular framework in one case, or a fibrous rete in another, implies 



1 I. c, p. 17. 



