Mr. Stokes on Orthocerata. 713 



A considerable difficulty exists in the examination of these fossils in many 

 cases, particularly in those where the substance of the fossil is replaced by 

 silex. A fracture, or a section by art, does not so clearly show the structure of 

 the fossil, as its exposure by the slow action of the weather; and hence we 

 greatly depend on accident for obtaining our information. 



In other cases, the substance of the shell is entirely wanting, and vacant 

 spaces alone represent the form of the fossil. This has been noticed in the 

 Actinoceras Bigsbii U'om Thessalon Island; and the same thing is constant 

 in regard to the septa of Baculites found at Maestricht. It may perhaps be 

 worth consideration, whether the nature of the substance of which these parts 

 of the animal was composed, has much influence on the preservation or non- 

 preservation of them in the fossil state; and I would suggest that it is always 

 worthy of observation, what is the condition of the greater number of other 

 fossils found in the same rock. In the case of Maestricht, we find some shells 

 and corals and the crusts of crabs preserved ; but the septa of Baculites are 

 always wanting, although sometimes we can find traces of their thin external 

 shell. I notice this, however, merely for the purpose of exciting observation, 

 because I am not aware if it has ever been made a subject of inquiry. 



If, from what has here been stated, it shall appear probable that the Hu- 

 roniae are the remains of Orthocerata, and that the shelly part of some of the 

 animals of this family was so thin as to have been generally destroyed, we 

 shall be led to the belief that the fossils figured in Dr. Bigsby's paper, at PI. 

 XXX. of Vol. i. Geol. Trans., 2d. Series, also belong to Orthocerata; and 

 though there is not evidence to establish conclusive proof that they were so, 

 yet the conjecture becomes more probable, from our inability to associate 

 these remains with any other known organic structure. 



These would open to us a great variety of forms for the animals of the 

 OrthoceratidcB, in addition to those indicated by the different forms of the de- 

 cidedly chambered shells with siphuncles, which are found in the older rocks, 

 of which there are many undescribed kinds, and which have always been at- 

 tributed to this family. 



We find these remains sometimes of conical shape, tapering rapidly ; some- 

 times curved, and at other times of great length, and tapering very gradually. 

 The animals to which they belonged were, no doubt, the Carnivora of the 

 ancient seas, in the mud of which their remains have been preserved, along 

 with those of contemporaneous animals of species on which they preyed ; and 

 it is of some interest to imagine an abundant variety in their forms as great as 

 was that of the Saurians of a later period, when that race of gigantic devourers 

 was called into existence. 



