310 Dr. m B. Holl—On Fossil Sponges. 



has never received that strict treatment of which it seems capable. 

 Much has yet to he done towards the attainment of a better know- 

 ledge of their structure, mode of growth, and variation in form 

 within the limits of the species, and not until this has been accom- 

 plished can a right understanding of the true affinities of the several 

 members of the group be arrived at, or any successful attempt 

 made at arrangement of the species and genera. 



The little interest which appears to attach to the study of fossil 

 sponges may possibly be due, in great measure, to the difficulties 

 which lie in the way of a rigid determination of the species. This 

 is owing to the inconstancy of the characters on which specific dis- 

 tinctions have been based; and consequently an enormous number 

 of species have been created, the described characters of which are, 

 in many cases, equally applicable to other forms, which are, never- 

 theless, totally distinct. Hence the subject is involved in a confusion 

 which is rendered still more" perplexing by the circumstance, that 

 many of the original types on which the descriptions were based can ° 

 no longer be traced. The means, therefore, of identifying the species 

 is by no means easy, and in some cases it is impossible to identify 

 them. As an example, we may mention the Spongites clavellatus, 

 Mantell, from the Chalk, of which there are two distinct forms, the 

 one composed of a network of inosculating fibres, the other con- 

 stituted entirely of branched and tuberculated sjoiculas. The same 

 may be said of the sponges included in the genera CJbenendo'pora, 

 D'Orb., Ciupulospongia, D'Orb., etc., some of which are spicular, and 

 others fibrous, and yet are precisely similar in their general appear- 

 ance. In all these cases there are no means of clearing up the 

 doubt, except by reference to the original type. 



Like their living analogues, the fossil sponges are liable to great 

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

 the remarks of Dr. Bowerbank on this subject are equally applicable 

 to the extinct as to the living species.^ 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 geolo- 

 gical position, has been thought sufficient for the creation of distinct 

 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 

 differentiating the sponges, and the consequent difficulty experienced 

 in framing specific descriptions precise enough for their identifica- 



^ " 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 normal form, it is rarely thoroughly developed until the 

 animal has reached its full maturity." Spongiadce (Eay Soc.) vol. i. p. 3. "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. 166. 



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