Harvey B. Holl — On Fossil Sponges. 60 



.Oh Fo.'<.-''d Sponges. — [From the London Geological Magazine, vol. ix., 



pp. 309-343, July and August, 1872. By Harvey B. Holl, M.D., 



F.G.S.] 



I. Introduction. — It has been said, with some degree of trufh, 

 that our knowledge of the low^er forms of life has advanced 7)a7-ipass». with 

 the improvements in the construction of microscopes ; and, no douV)t, 

 very considerable progress has been made in some departments of 

 investigation within the last few years. In the vegetable kingdom 

 more especially has this been the case; and with respect to animals, 

 the structui-e of the Protozoa has been especially elucidated by able 

 observers, the Spongiadne chiefly by the labors of Dr. Bowcrbank. 



Among the lower forms of extinct life progress has necessarily been 

 slower, especially as regards the sponges ; for although new forms have 

 been described from time to time, the group collectively has never 

 received that strict treatment of which it seems capable. Much has 

 yet to be done toward the attainment of a better knowledge of their 

 structure, mode of growth, and variation in form within the limits of 

 the species, and not until this has been accomplished 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 

 sptniges 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 distinctions 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, nevertheless, totally dis- 

 tinct. 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, \vc 

 may mention the Spongites elavellatus, Mantell, from the chalk, of which 

 there are two distinct forms, the one composed of a network of inoscu- 

 lating fibers, the other constituted entirely of branched and tubercu- 

 lated spiculte. The same may be said of the sponges included in the 

 genera Ckenendopova, D'Orb., Cupidospongia, D'Orb., etc., some of 

 which are spicular, and others fibrous, and yet are precisely similar in 

 their general appearance. In all these cases there are no means of 

 clearing up the doubt, except by reference to the original type. 



