CUCULL^A. 



by an obtuse angle, so that when tlie two valves are closed, 

 and that side alone is observed, it is cordiform, and lon- 

 gitudinally elevated in the middle : the umhones distant, 

 separated by the area to which the external ligament is 

 attached ; two muscular impressions in each valve, of 

 which the anterior one is elevated, with a sharp edge, or 

 produced into the shape of a little ear. Hinge linear, 

 straight, furnished with numerous, rather irregular, trans- 

 verse teeth ; and at each extremity, from two to five more 

 elongated teeth, lying in a nearly parallel position with 

 the line of the hinge. The ligament is external; it does 

 not cover the whole area between the two umbones, a 

 small portion of the anterior side remaining uncovered ; 

 the area itself increases by age, and becomes transversely 

 grooved. 



The dissimilarity betv/een the two valves was not ob- 

 sei'ved by Lamarck, nor is it mentioned, as we believe, 

 by any Avriter; it is not great, but is observable in several 

 circumstances, the larger valve, into which the other falls, 

 being more deeply coloured, and altogether more strongly 

 marked on the inside, while the smaller one, which is paler 

 in colour, has its longitudinal external striae more distinct 

 and close set, than those on the other valve. We have 

 reason to believe, that the Cucullaeag are naturally covered 

 with an epidermis, though this is, for the most part, cleaned 

 off before they are brought into commerce. 



We are only acquainted with one recent species of 

 Cucullaea, nor has Lamarck described m.ore; it is the Area 

 Cuculliis of Gmel. Cucullcea auriculifera, Lam. in this the 

 teeth are finely, perpendicularly striated. The fossil species 

 are, however, much more numerous; of these, one is de- 

 scribed by Lamarck, the C. erassatina, it is found in the 

 neighbourhood of Beauvais and at Bordeaux, in beds 

 similar to that of Grignon ; but in England several species 

 occur, both in the Green sand and in the inferior Oolite, 

 they are engraved in Sowerbi/''s Mineral Coneliology : those 

 of the inferior Oolite, are also found at Bayeux, in Nor- 

 mandy. 



Fi^. 1 Ciicnllcea auriculifera, Lam. 



2 inside of one valve of the same, 



3 front view of the hinge of the same. 



4 decussata, Park. 



