6G Harvey B. Holl — On Fossil Sponges. 



Like their living uimlogues, tlie fossil sponges are liable to great 

 variation in form, and other external and obvious characters ; and the 

 remarks of Dr. BoAverbank on this subject are equally applicable to the 

 extinct as to the living species : ["There is no class of animals in -which 

 the form varies to so great an extent (as the living sponges) according 

 to difference of locality or other circumstances ; and even where there 

 is a striking noi'mal form, it is rarely thoroughly developed until the 

 animal has reached its full maturity." Spongiche (Ray Soc. ) vol. 1, p. 

 o. "As a generic character, form is inadmissible, inasmuch as each 

 variety of it is found to prevail indiscriminately in genera differing 

 structurally to the greatest possible extent.' [Ibid, p. 156.] Yet, on 

 external characters alone nearly all the generic and specific distinctions 

 of the fossil sponges have been framed, and very slight variation in 

 external configuration, in the disposition of the oscules, or even in the 

 geological position, has been thought sufficient for the creation of dis- 

 tinct species. Nevertheless, if we except the Foraminifera, there is 

 no class of animals in which the outward characters are less stable, 

 and like these, in conformity with the same low state of organization, 

 there are none that have enjoyed longer range in geological time. 



The insufficiency of mere external character for the purpose of dif- 

 ferentiating the sjDonges, and the consequent difficulty experienced in 

 framing specific descriptions precise enough for their identification has 

 been long felt. This renders it desirable to discover, in the miuuter 

 structure, characters of a more permanent nature. With respect to 

 the living s.ponges, this has indeed been done, more or less successfully, 

 by Dr. Bowerbauk. He finds " in the skeleton and in the form and 

 disposition of the spiculie, characters which, however Protean the form 

 and color of the sponge may be, can always be recognized with cer- 

 tainty." Can the same means be made available for the extinct spe- 

 cies ? Obviously there will be many difficulties in the way, for in the 

 latter we have to deal with the skeleton alone, modified by fossilization ; 

 whereas in the former all the structures are in a condition admitting; of 

 minute investigation. Nevertheless, very conimonly, enough of the 

 minute structure can be made out in the fossil to render it a most im- 

 portant means of discriminating the species. The external appearance 

 is all Init valueless for this purpose. 



II. Prior to the time of D'Orbigny no attempt had been made to 

 systematize the genera established by Lamoureux, Goldfuss, De Blain- 

 ville, Michelin, Reuss, and others. M. D'Orbigny, however, conceiv- 

 ing that the fossil sponges had for the most part an organization en- 

 tirely distinct from that of the recent species, divided De Blainville's 

 class Amorphozoa, into two orders, viz., the Jwrnyand the stony sponges. 



