Harvey B. Holl — On Fo^nl Sponges. 79 



to the thickness of the rays and at the points, and the occurrence of 

 radiate spicula in the same individual sponge of all sizes, from the ma- 

 tured condition down to extreme smallness, always preser\nng the 

 radiate form, is entirely again<t the view of M. Etallon. If union 

 ever takes place, it is probably the result of fi^silization, in cases where 

 the points of the rays are in contact, and it is then brought alx)ut, 

 probably, either by adventitious deposit or in the replacement of the 

 original structure — the mineral which has infilled the mould has run 

 together. 



Nevertheless, the labors of ^I. Etallon are a move in the right direc- 

 tion, and it appears probable from his' research, that by a careful inves- 

 tigation of the structural details of the fossil sp)uges, it may be possible 

 ultimately to arrive at results whicli may lead to an arrangement of the 

 species and genera more suited to the requirements of the day than the 

 artificial systems of D'Orbigny and DeFromentelle. The time, however, 

 is probably not yet come for this to be attempted, the more especially 

 as the arrangement of the reoent species is far from being settled. 



V. Two conclusions are suggested by the foregoing remarks : 1st, 

 that the present state of the fossil sponges aflSjrd no certain indication 

 of theif condition during life ; and 2d, that in the diSerentiation of 

 the genera and species the same principles must l>e kept in view in the 

 fossil as in the recent sponge. Some of the oldest fossil sponges were 

 as highly organized, apparently (if the term is admissable to these 

 humble forms of life}, as those of the present day, as for instance Pro- 

 to-ipongia of the Lingula Flags and Ludlow Rocks, the Silurian lidiadites, 

 and the Devonian Sphcero.'^pongia te.<*erata. The Protospongia, iu fact, 

 belong to that general type of Cyathiform sponges, formed of elongated, 

 vertical, and horizontal rods or fibers, which become more abundant in 

 the Oolitic and Cretaceous rocks, and have their representatives even 

 iu the present day. 



The Amorphospongidse first make their apj)earance in the Silurian 

 rocks, and occur more or less abundantly in the calcareous marine 

 deposits of all the succeeding epochs ; and species are still living in 

 our present seas, for which, as far as external appearances are concerned, 

 at any rate, it is difiicult to find good distinctive characters. The 

 cup-shaped and cylindrical forms of this group commence in the Devo- 

 nian and carboniferous limestones, and in the Mortiera rertebralU (De 

 Konninck), we have a depressed form of the latter, which, in the moun- 

 tain limestone (?) of India attained greater vertical development. 

 There are recent forms, which, to all appearances, are undistinguishable 

 either in figure or in the texture of the rete, and the only appreciable 

 difierence that can exist mu-t be in the structure of the fiber. SipJio- 



