166 REPORT — 1856. 



who would study species in a comprehensive manner might advantageously 

 consult the canons given in Dr. W. B. Carpenter's Researches on Orbitolites, 

 'Trans. Roy. Soc' 1855, pp. 226-230. It must not be expected, however, 

 that creatures (comparatively speaking) so highly organized as mollusks, 

 should assume such abnormal forms as the lower animals and plants. Often 

 indeed one species will greatly vary, while another, closely allied, is constant 

 in its characters; or differences will be found between the shells of a single 

 species, which in another tribe would justly entitle them to generic separa- 

 tion. No general rules therefore can be given to guide the student. But it 

 is required of him that he should faithfully use all the materials at his com- 

 mand ; not being satisfied with an examination of particular forms, but care- 

 fully working through those shells especially which many would cast aside 

 simply because they were puzzling, or were not fine specimens. Those 

 whose work lies mainly among picked collectors' shells are recommended to 

 study the series of fossils arranged by Prof. E. Forbes in the Museum of 

 Practical Geology, and the large suites illustrating particular species in the 

 British Museum Mazatlan Collection. 



19. It is, however, by no means recommended that we should abstain 

 from describing new forms, because it may afterwards be discovered that 

 they are conspecific with others previously found. The great point is, that 

 we should be guided in those matters that are least known by the experience 

 gained by studying carefully ascertained species in their varied develop- 

 ments ; and that we should not desire the maintenance of species simply 

 because they have once been published, when further light assigns to them 

 a subordinate place. Those writers are therefore not to be blamed who 

 have multiplied species simply from a want of sufficient materials. Thus 

 when C. B. Adams described as five distinct species the Ccecum pygmceum> 

 diminutum, monstrosum, ebur?ieum, and Jirmaium, which seem only stages in 

 the development of the same shell, he did carefully, according to the then 

 state of knowledge, what a naturalist of less accuracy would have passed 

 over as one shell, simply from not having found out the differences. But 

 when the further discovery of many hundreds of individuals proves that they 

 are identical, a higher point of knowledge is reached, according to which all 

 examinations in the same group may be henceforth interpreted till some yet 

 higher generalization is attained. 



20. But when species are constituted or disregarded, simply in obedience 

 to a theory, injury is done to the progress of science. Thus a recent author 

 on the British Fauna appears unwilling to believe in the existence of species 

 other than what occur on the South Devon coast; and accordingly unites 

 together many which have been constituted by the most accurate naturalists, 

 but which, from their northern station, he had not an opportunity of study- 

 ing. And on the other hand, the principal American conchologists, having 

 assumed a theory that no species can be found in two distinct provinces 

 unless we can see a way by which they may have moved from one to the 

 other, forthwith proceed to describe as new everything which makes its ap- 

 pearance on an unexpected side of the coast. Undoubtedly it is by far the 

 most easy way of studying a fauna merely to consult those works which 

 apply to that fauna, and to describe as new whatever is not found therein; 

 but we must beware lest we be forcing Nature into our own form. Now, 

 just as we give a species already constituted the benefit of a doubt, till we 

 be fairly able to prove its identity with another, so we may suppose shells 

 different from opposite coasts, till we can prove them the same. But, in the 

 language of the late Dr. Binney*, " until the question of the identity of 



* Terrestrial and Air-breathing Molluscs of the United States, edited by Dr. Gould, Boston, 

 1851, vol. i. chap. 3. 



