CRENATULA. 



Lam, — Ann. du Mus. vol. 3, p. !?5. 



TESTA subaequivalvisj complanata^ lamellosa^ 

 subirregularis. Cardo lateralis^ linearis, margi- 

 nalise interne crenulatus, crenis in seriem ordi- 

 natis^ eallosisj subexcavatisj ligamentum excipi- 

 entibus. 



Not a single shell of this Genus do we find represented 

 until Lamarck instituted it in the third volume of the 

 Annales du Museum, if we except a bad figure in Chemnitz, 

 V. 7, t. 58, f. 175. Lamarck's account of the Genus is ac- 

 companied by representations of two species, and in his 

 Hist. Nat. des Anim. sans vert, he has described several 

 more, nevertheless, on account as we suppose of the 

 irregularity of the shell, we have experienced considerable 

 difficulty in deciding to which species those engraved in 

 our plate belong, nor dare we now mention them as posi- 

 tively decided ; indeed, we think there is need of much 

 caution in determining the species of Genera, subject as 

 this is to much variation in form. We have been led to 

 the determination which we have adopted, by the dif- 

 ference in the form of the inner pearly portion of the shell, 

 which does not seem to be subject to the same degree of 

 variation with the outer foliaceous portion. In the form 

 of this part, the small shell, fig. 2, agrees with Lamarck's 

 C. mytiloides, and the two larger with his C. avicularis. 



The Crenatula, figured by Chemnitz, is arranged with 

 Ostreu by Gmelin, from which, however, it is easily dis- 

 tinguished by its crenulated linear hinge ; it is much more 

 nearly allied to Lamarck's Perna^ and we formerly ventured 

 to hint the possibility of their identity, but we nOw think 

 it is distinct, for Perna is strongly characterized by a sinus 

 for the passage of the byssus, which Crenatula has not. 



