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 shell of Sepia. 

 " Its structure," the authour observes, " is altogether peculiar, and may 

 perhaps be explained by saying that as in Sepia lamellce 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 moUusk, 

 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 I believe therefore that the animal cannot be 

 referred to the true Jlcephala. 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 Mollasca, 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. It does 

 not contradict the time when the animal existed as a living form. W^ere 

 Kautilus and Spirula not extant in our living creation, what should we 

 say of .Ammonites and Eelemnites? jiptijchxis lived along with these. 

 How shall we comprehend Ornithocephalus or Pterodactylus within the 



