BELLEROPHON. 



TESTA spiralis, involuta, crassa, utrinque 

 uinbili(tata, ferh symmetrica, apertura maxima, 

 semilunata, dorso rotiindato, obtuse bicarinata, 

 inter carinas emarginato. 



In general external forna like the JSTautilus, but destitute 

 of chambers and in its peculiar characters approaching 

 nearly to Argonauta; this remarkable shell, only known 

 in the oldest fossiliferous strata, should be placed next to 

 the latter Oenus, from which it differs only in two im- 

 portant particulars, namely, in its nearly globular form 

 and in having a thick shell. It is the only fossil that 

 bears any real resemblance to Argonauta ; although many 

 Ammonites have occasionally been regarded as fossil Argo- 

 nautse, merely on account of their resemblance in form 

 to the Paper Sailor. That the animal which forms this 

 shell must very closely have resembled that of the Argo- 

 nautae, and that both (whenever they may be discovered) 

 will prove to be nearly like that of Carinaria we think 

 there can be no doubt: we are, therefore, satisfied that 

 neither can have been formed by a cephalopodous animal. 



It may not be amiss to detail here the principal reasons 

 we have for drawing the above-mentioned conclusions ? 



Fi7'stly, The animals of ail the testaceous mollusca are 

 affixed to the interior part of their shell by one or more 

 muscles. 



Secondly^ They are covered (beneath the epidermis, 

 wherever an epidermis exist) with a mantle from which 

 the testaceous matter is deposited; which mantle covers the 

 animal within the shell. 



Thirdly/. The shell in all univalves covers the im- 

 portant viscera such as the liver, the ovaries, &c. 



Fourthly. It is important to make the observation, that 

 in spiral univalves, such parts of the mantle as cover the 

 inmost portions of the animal, are always comparatively 

 thinner than the other parts of the mantle which may be and 



