86 Mr. Toiilmin Smith on the Classification IV. — On the Ventriculidse of the Chalk; their classification. By J. TouLMiN Smith, Esq. [Continued from vol. xx. Ist Series, p. 191.] I HAVE thus described with some detail the structure which marks a large group of fossils from the chalk, and have further endea-voured to show what are the natural affinities of the group thus marked. The only clue has thus been obtained towards arran-ging, in a true and natural classification, those widely varied forms to which, under various secondary modifications, this structure belongs. The few of these which have hitherto been known have been uncharacterized except by names as various as the different writers, and which, being names merely, could leave no impression of reality on the mind of the inquirer. It will assist the inquirer, and will much enhance the import-ance of the present investigation, if, before entering on the de-scription of their modifications, something is said of the strati-graphical distribution of these fossils. From what has already been stated, it will be obvious that these fossils require to be sought : they can seldom fall in the collec-tor's way as do fossils having solid parts, Testaeea, Vertebrata, &c. If found at all in the hands of the dealer they will usually be fragmentary only, or in a matrix, the flint, the deceptive character of whose obvious appearances has been already shown. By far the greater part of the forms assumed are, besides, such that no blow of the hammer can disclose the character of the fossil. It is necessary to premise thus much that it may be under-stood that the fact of these fossils not having yet been recognized in particular localities or strata is no proof that they do not exist therein ; and, now that the true structure characteristic of them has been described, it may be hoped that the presence of some representatives of the family may be detected much more widely than has been hitherto suspected. A mere fragment may now serve for the detection of that presence*. As far as can be gathered from the various authorities already cited, it would appear that these fossils are more abundant in England than in any other country. In the chalk of Kent, Sussex, Norfolk, Wiltshire, and the respectively adjoining locali-ties, some of the forms are abundant, though in each region the localities in which they abound are certainly restricted. In the chalk of Yorkshire they appear to be much less abundant. In-deed many bodies which have heretofore been grouped as Ventri-culida from that region have no relation to that family ; while * Of course not for the determination of species, or, necessarily, even of genus.
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