2 BRITISH JURASSIC GASTEROPODA. 
other Microzoa generally have received a large share of attention, the Mollusca 
seem to have been comparatively neglected. On the other hand, the Vertebrata 
have always had a number of eminent exponents, whose work has rendered the 
publications of the Paleontographical Society of peculiar value and interest. 
On the whole, the great age of molluscan paleontology, as evinced by such 
works as those already quoted, preceded the announcement in England of the 
doctrine of Evolution by about ten years. It is true that this doctrine, now so 
universally accepted, had been most ably pre-figured by Lamarck and others ; 
yet it had met with little favour from biologists or paleontologists previous to 
the appearance of Darwin’s great book. Hence the age of Goldfuss, of D’Orbigny, 
and of Morris and Lycett, was an age when the general faith in distinct creations 
was at its height. This is what Professor Marsh calls the third period in paleon- 
tology,’ when a species was regarded as a rigid entity, and he who “ made” or 
described a species acquired a sort of prescriptive right therein. ‘So long as the 
bulk of naturalists really believed in the immutability of species there was 
something dangerously fascinating in the prospect of finding out and describing 
a form-group, which was destined to endure no change, which might indeed be 
destroyed or die out but could never be altered. The maker of a new species 
would thus come to look upon his offspring with almost parental solicitude, and 
having stood godfather to his own child would attach to the name given by him 
a peculiar interest.’”” 
Perhaps the belief of that day was on the whole favourable to accurate 
definition, and there is no doubt that the practice adopted by some collectors of 
burking doubtful forms and varieties rendered it more easy to constitute and 
define “species.” It must, however, be allowed that, when once the doctrine of 
Evolution is admitted in its entirety, the ideas attaching to such expressions as 
“genus” and “species” lose somewhat of their definition. Nevertheless they 
are necessities in classification ; and even if they do not absolutely exist in nature, 
it becomes necessary as by a sort of legal fiction to presume that they do exist for 
purposes of scientific arrangement. But the paleontologist has to deal with the 
element of time in addition to his other difficulties, and thus for him, far more 
than for the malacologist, does it become necessary not to place too rigid a 
meaning on “ genus” and “ species.” 
I fear that this will appear somewhat heretical even in these days of belief in 
Kvolution; but, as very justly observed by Professor Cope, the fact that all 
definitions which separate adjacent groups will be ultimately found to be fallible 
does not permit us to fall “into inexact and inconsistent methods of definition.” 
Hence the work of definition need not be slovenly because we no longer believe 
‘ “ Address before the American Association for the Advancement of Science, 1879.” 
? W. H. Hudleston on the Yorkshire Oolites, ‘Proc. Geol. Assoc.,’ vol. v, p. 460. 
