61 



Although diificuities may attend the attempt to arrange, 

 by these characters, substances so vaguely formed as the 

 alcyonia, especially those which exist in a fossil state ; yet 

 it will be found that the above table will afford considerable 

 advantage to the student of fossils. He will, by a com- 

 parison with the characters of the species as there given, 

 and b}^ attention to the following observations, gain a nearer 

 approximation to the true character of the substance under 

 examination, and will be frequently enabled to give to it a 

 name and place. 



Whilst endeavouring to make the required distinctions 

 in fossils of this kind, difficulties must arise from the ina- 

 bility which is frequently found of ascertaining, in fossil 

 specimens, the nature of their texture ; it sometimes hap- 

 pening that no assistance can be yielded either by the form 

 of the fossil or by the appearance of its surface. The am- 

 biguity arising from the form depends on the fossils of this 

 genus being sometimes found under the same specific forms 

 which belong also to Spongites, Syphonites, and Mantellites : 

 this is particularly the case with the cyathiform and fruc- 

 tiform species, which may be found in all these genera. 



There are therefore four distinct genera under which 

 fossils bearing the same general forms may be placed ; and 

 the characteristic marks of each genus will, in general, be 

 found sufficiently evident on their surfaces to mark the 

 situations which, in classification, each of them should hold. 



If a cellular texture, such as would be formed by the 

 irregular decussation of membranous substance, can alone 

 be traced, without any appearance of tubuli, the place of the 

 fossil would appear to be under the genus sponge ; but if, 

 in addition to the spongeous texture, straight or regularly 

 divaricating simple tubuli should appear, its place would 

 be under syphonia. If, whether spongeous texture appear 

 or not, simple tubes are discovered connected laterally either 

 by anastomosing or intercurrent tubules, the fossil may be 



