10 Panama Shells. introduction, 



taohed to dead shells within the aperture, render it one of 

 those which are least exposed to such accidents. 



The following is a list of the principal pairs of analogues 

 which inhabit both sides of the Isthmus. The list might be 

 increased, especially by comparision of the very minute 

 species. But the group, as it is, presents such a variety in 

 respect of size and characters, of habits of station, tenacity of 

 life, &o., as to render it incredible that they all should owe 

 their distribution in pairs to tt. common process of transporta- 

 tion. Cyprsea oervinetta occurs only beneath large rooks, at the 

 low water mark of the spring tides, and lives but a short 

 time when removed from the water, and Strombus gracilior 

 is pelagic ; and the others live at or near low water mark 

 on rocks, under stones, in sand, in fine mud, &c. In gene- 

 ral the derivation- of analogues from a common stoolv is more- 

 over inconsistent with the existence of analogues which are 

 antipodes to each other. 



Panama. ^Jamaica. 



Cyprsea cervinetta ; C. exanthema, 



Marginella minor ; M. minima. 



M. sapotilla ; M. prunum. 



Mitra nucleola ; M. granulosa. 



Oliva araneosa ; 0. reticulata. 



0. venulata ; 0. soripta. 



Purpura undata ; P. fasoiata. 



Columbella guttata ; 



C. cribraria Lam. 

 C. parvula Dunker. 

 Cassis abbreviata ; C. inflata. 



Oniscia tuberculosa ; 0. oniscus. 



Strombus gracilior : S. pugilis. 



Triton vestitus ; T. pilearis. 



Murex erosus ; M. intermedins. 



Pyrula patula ; P. melongena. 



* These Oarribbean species have all been collected by us in Jamaica. 



