On the Bilobite. 41 



this figure is compressed in such a manner as to produce a 

 crest, and approximating it nearly to the figure of a Tri- 

 lobite. 



The under surface is extremely irregular. The edges, as 

 before mentioned, are very thin, and are elevated about two 

 lines above the inferior surface ; this, however, is not uniform 

 throughout its whole circumference ; the anterior extremity, 

 comprising one-third of the whole fossil, is without such a 

 raised border. In this part, the costa? of the dorsal surface 

 are continued beneath, and meet each other at angles of about 

 45°. The line of junction has not yet been made visible by 

 the most careful dissection. The remaining two-thirds, or 

 posterior part of the under surface, presents a series of concen- 

 tric lines, interrupted as at fig. 4. by a carina directly beneath, 

 and in the direction of the superior or dorsal furrow. 



Various conjectures have been hazarded respecting the origin 

 and nature of these organic relics. 



A perusal of the learned work of Brongniart* on theTrilobites 

 connected with their peculiar appearance, led to an investigation 

 whether they might not be analogous productions belonging 

 to the order of Crustacea, but without any satifactory result. 

 Neither eyes, nor antennae, nor feet, could be detected, after a 

 careful investigation, and dissection of several specimens. 

 They have been by many supposed to be the leaves of plants, 

 such as Ferns, he. ; but their thickness, and perhaps their as- 

 sociation, with decided animal remains, would weaken this 

 conjecture. 



Another opinion, which is advanced with diffidence, is, that 

 these remains may be moulds or casts of an extinct species of 

 Cardium. This belief has been strengthened by an examina- 

 tion of the Cardium hibernicum, as figured in Sowerby's Mi- 

 neral Conchology, vol. I. p. 187.pl. 82. With these views, the 



* Histoire Naturello dosCntstaces fossilcs, &c. par Alexandre Brong'ni- 

 art. Paris, 1822. 



