488 Analytical Notices of Books. 
objects that when the two halves, into which they are subdivided, are 
-brought into contact they meet only at three points of their margin; 
that there is no trace of muscular impressions on their surface; and that 
their hinge, or point of connection between the valves, is of a totally 
different character from that of any known bivalve. On treating the 
fossil with diluted muriatic acid, its calcareous portion was dissolved, 
and the skeleton which remained was found to be porous and cellular, 
and forcibly called to mind the structure of the internal sheil of Sepia. 
*¢ Tts structure,”’ the authour observes, ‘‘is altogether peculiar, and may 
perhaps be explained by saying that as in Sepia /amelle of horn, so in this 
case cells of horn, are filled with a calcareous substance.’’ This curious 
mode of formation is described with much detail in the paper, to which 
we must refer for many valuable observations on this and other points. 
But the discovery of evident traces of the soft parts of the animal leads 
to considerations of still higher importance, ‘ The structure of the 
shell” according to our authour, ‘* speaks not only of a molluscous 
animal in general, but also indicates with certainty a naked mollusk, 
the shell being internal. We can only further enquire whether this 
naked mollusk belongs to the Gasteropoda or the Acephala? For 
answering this question we possess again no other materials than the 
shell. As we have seen, it is formed, in its characteristic parts, like an 
imperfect bivalve, and J believe therefore that the animal cannot be 
referred to the true Acephala. As regards the determination of the 
anterior and posterior sides, and the position of the head, I must refer 
to an unfinished work of mine, treating of the metamorphosis of the 
shells of Mollusca, in which I shall also develope my views with respect 
to the normal position of the shell. We have thus the type of a 
molluscous animal, such as none has yet been found. May not this be 
regarded as improbable or somewhat far-fetched. But this view has offered 
itself to me after a careful treatment and examination of its parts. Itdoes 
not contradict the time when the animal existed as a living furm. Were 
Nautilus and Spirula not extant in our living creation, what should we 
say of Ammonites and Belemnites? Aptychus lived along with these. 
How shall we comprehend Ornithocephalus or Pterodactylus within the 
