418 



PATELLID^E. 



It would seem to be a law in both animal and vegetable 

 kingdoms that no character, whether of structure or form, 

 preserves an equal value in every tribe, but varies in its 

 importance ; in one group characterising a class, in another 

 scarcely determining a species. Important as the ar- 

 rangements of the respiratory system are among the 

 Mollusca, we have an example in the family before us 

 of their degradation to a mere generic value. Cuvier as- 

 sociated the Chitons and Limpets in one order distinguished 

 from all other sections of the Gasteropods by the dispo- 

 sition of the branchial leaflets, yet no malacologist who 

 attends closely to the conformation of the soft parts 

 in Chiton and Patella, would hesitate, in the present 

 state of our knowledge, to maintain that the latter genus 

 had more affinity with Acmaa and its allies, than 

 with the former, however different the branchial arrange- 

 ments appear. The difference is more in appearance than 

 in reality ; and the resemblance between the branchial 

 arrangement of Chiton and Patella, in like manner, is more 

 apparent than real, although Cuvier mistook it for an 

 indication of affinity. The cyclobranchiate gill of Patella 

 seems to us a single long branchial plume, exserted from 

 the cervical cavity, and coiled round between mantle 

 and foot. Without going so far as Professor Loven, who 

 has united the entire shelled patelliform Mollusks in one 

 genus, we feel bound on anatomical and phjsiological 



