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. 



