MOLLUSCA. 93 



ternally." But many new genera must be instituted, to 

 embrace all the fossil species which would have been re- 

 ferred by Linnaeus to the genus Anomia. 



16. MYTILUS. Before proceeding to notice those new 

 genera which have been formed from the Linnaean mytili, 

 we may state, that the three parasitical species of the Sys- 

 tema Naturce, belong to the genus Ostrea, to which they 

 have been transferred by late authors. But improvements 

 of a more important kind have been effected. Linnaeus had 

 associated together in this genus both fluviatile and marine 

 shells- The former now constitute a very natural genus 

 termed ANODONT A, formerly referred to, of which the British 

 rivers furnish several species. The muscular impressions 

 are three in number. 



It was easy to perceive that the mytilus hirundo of Lin- 

 naeus did not belong to the true mussels, it being an in- 

 equivalve shell. Accordingly Lamark has constituted a new 

 genus for its reception, which he terms AVICULA. The 

 mytilus margaritiferus of Linnaeus is of this genus. 



Lamark, by restricting the characters of the genus myti- 

 lus to include such species as have the beak terminal, has 

 in this manner separated the transverse species to form the 

 genus MODIOL.A. The mytilus modiolus of Linnaeus is the 

 type of the genus. It is common on the British shores, 

 together with the modiola discors and discrepans. We are 

 at a loss to account for the scruples of Lamark (Annales 

 de Museuss, vol. x.) about considering this genus as byssi- 

 ferous. Had he ever examined the figure of the type of 

 the genus in tab. 53 of Zoologia Danica, all his doubts 

 would have been removed. 



17. PINNA. No changes have taken place in this Lin- 

 naean genus, except that a few new species have been added. 



