370 
Mr. Toulmiii Smith on the Classification 
prevails. Numberless illustrations of design and adaptation 
have forced themselves upon attention in the course of the inves- 
tigation, and more might have been suggested had it not been 
feared that the allusion would appear obtrusive. 
It cannot be supposed that the forms which have been here 
described constitute all that existed of this family even in the 
cretaceous seas. In my own collection are a few individuals as 
to whose specific identity I have some doubt, but as to which I 
would wait for further means of observation rather than rashly 
increase the number of species. Doubtless, now that the struc- 
ture has been described, and figures and descriptions of such 
numerous forms been given, some attention will be directed to 
the subject and other forms be found. From the great extent of 
the materials on which these observations have been made, it 
may, however, without presumption, be conceived that the prin- 
cipal typical forms are here included, and that any which may 
hereafter be clearly ascertained will range themselves easily in 
one or other of the groups whose characters, general and special, 
have been here determined. 
Many other obscure fossils are found in the chalk, either gene- 
rally unknown or distinguished by names which impart little idea 
of vitality to the objects to which they have been attached, — a 
vitality which it is sought in vain to realize by any descriptions 
which have hitherto been published. To a more particular ex- 
amination of some of these, the attention of such readers as have 
followed with any interest the present inquiry into the structure, 
affinities and forms of the Ventriculidse, may, at a future day, be 
perhaps invited. 
EXPLANATION OF PLATES. 
[Plates VII. and VIII. appeared in vol. xx, of the first Series.] 
PI. VII. (all in flint except figs. 1, 2, 3, 9 and 12). 
Fig. 1. Transverse section of Cephalites longitudinaUs, pp. 89 & 281. 
— 2. Transverse section of C. alternana, pp. 89 & 283. 
— 3. Oblique section of C. bullatus, p. 284. 
— 4. Vertical section of Vc.ntric.uUfes, showing base of body lodged and 
ensheathed in the root : the upper part showing the fold of the 
membrane, p. 88. 
— 5 & 6. Vertical and transverse section of the same specimen showung 
body lodged and ensheathed in the root, p. 91, & see p. 362, note. 
— 7. Root seen externally ensheathing body, p. 91. 
— 8. Intimate structure of the Ventriculidae highly magnified, showing 
square and octahedral structure, p. 93. 
— 9. Cast in chalk of this structure, p. 95. 
— 10. The octahedral structure very highly magnified, p. 95. 
— 11. The dermis or underskin, pp. 95 & 182. 
— 12. The epidermis or polyp-skin, pp. 95 & 182. This s])ecimen is broken 
away at the upper part, showing traces of the structure below. 
