81 



4. C. elliptica. Convex on the upper part; stellated by obsolete 

 lamellae; with an elongated central groove. Guett. Mem. 

 vol. iii. Tab. xxi. fig. 17, 18. 

 Fossil. Perpignan. 



Only known as fossils. 



Lamarck observes, that this last fossil is the largest of 

 the known species of this genus, and that its oval or elliptical 

 figure is peculiar to it. The fossil here described is the 

 same as is figured, Org. Rem. vol. ii. PL x. fig. 1, 2, 3, 4, 

 and its nature inquired into, p. 113. 



The superior part of this fossil, possessing the longitu- 

 dinal groove, derives a smooth downy appearance, from 

 innumerably fine striae, formed by articulated fibres, which, 

 proceeding from the margin of the inferior surface, pass 

 round every part of the upper surface, and terminate in the 

 sides of the central longitudinal groove. The inferior sur- 

 face is nearly flat, and is marked by concentric linear ridges 

 and corresponding depressions, intersected by numerous 

 lines, radiating from the centre to the circumference. The 

 examination of this peculiar organization shews it to be 

 probable that it gave to this animal the power of fixing 

 itself, like the remora or sucking-fish ; whilst, by the opening 

 in its superior part, it alternately received and ejected the 

 sea water, the medium of its nourishment. 



Supposing the animal laid with its inferior surface, on 

 any substance wet with the sea water, the retraction of the 

 fibres upwards, about the centre of that surface, would 

 produce a vacuum between that surface and the surface of 

 the body on which the animal was placed ; such a degree of 

 adhesion would be thereby obtained, that no removal of it 

 from that spot could take place, whilst the vacuum was pre- 

 served. On the other hand, on the contracting of the per- 

 pendicular muscular fibres terminating on the edge of the 

 inferior surface, the edge would be raised ; air would gain 



M. 



