MOLLUSCA. 93 
ternally.” But many new genera must be instituted, to 
embrace all the fossil species which would have been re- 
ferred by Linnzus to the genus Anomia. 
16. Myritus. Before proceeding to notice those new 
genera which have been formed from the Linnean mytili, 
we may state, that the three parasitical species of the Sys- 
tema Nature, belong to the genus Ostrea, to which they 
have been transferred by late authors. But improvements 
of a more important kind have been effected. Linnzeus had 
associated together in this genus both fluviatile and marine 
shells. The former now constitute a very natural genus 
termed ANoponTa, 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- 
neus 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 Avicuta. The 
mytilus margaritiferus of Linnzus 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 Moprota. The mytilus modiolus of Linnzus is the 
type of the genus. It is common on the British shores, 
together with the modiola discors and diserepans. 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. Prywa. No changes have taken place in this Lin- 
nan genus, except that a few new species have been added. 
