ON MOLLUSCA OF THE WEST COAST OF NORTH AMERICA. 353 



entered on the fauna, if it could be shown to have been picked up on British 

 sands. There are two main sources of information for the comparison of the 

 faunas : — (1.) The collections of Mr. Nuttall and M. Reigen ; and (2.) 

 those of the Mexican War naturalists. Now with every respect for the 

 labours of the latter gentlemen, who doubtless did the very best that it was 

 possible for them to do under their peculiar circumstances, we hesitate 

 before we receive from that source alone results at variance with the former. 

 And for this simple reason ; that Mr. Nuttall did not travel further south 

 than San Diego, nor did M. Reigen pass beyond the district of Mazatlan : 

 while the officers were moving from place to place, and liable to the errors 

 that even peacable naturalists may make under such circumstances. As the 

 results of their collections have been carefully tabulated above, those who 

 place implicit reliance upon them can easily add to the lists accordingly : but 

 we think it a sufficient ground for hesitation, that no less an authority than 

 Dr. Gould had formed the opinion, judging from these collections alone, that 

 Mazatlan belonged to the Californian rather than the Panamic type ; the 

 contrary of which is abundantly proved by the Reigen collection. It appears 

 also that Prof. Adams entertained the same doubts, though he does not ex- 

 press them ; for while he quotes the war-naturalists for seven of his Panama 

 species as inhabiting Upper California, he says in his introduction that none 

 of the species of the province inhabit San Diego, which is at the borders of 

 Lower California. The following are the species common to Mr. Nuttall's 

 and M. Reigen's collections, the specimens quoted from the latter being all 

 that were found out of several myriads of shells. 



Californian Fauna. 



Species. 



Gulf Fauna. 





1. 



2. 

 3. 



4. 



5. 

 6. 

 7. 



8. 



9. 

 10. 



12. 

 13. 

 14. 

 15. 

 16. 





Not common. 



Very rare. 



Two minute dead valves, possibly 



the fry of this species. 

 One pair and a valve, probably of 



this species. 

 Typical. 

 Very rare. 

 Very common, 

 A very few, resembling B. nehu- 



losa, but possibly = 5. Adamsi, 



var. 

 2 sp. (? ballast). 

 1 sp. (? ballast). 

 1 sp. (? ballast). 

 Typical, widely diffused. 

 Typical, widely diffused. 

 Extremely rare. 

 Typical, common. 

 Var. Pritchardi. 







Typical and abundant . 

 Typical 



Trigonella crassatelloides ... 

 Chama exogyra 



One young sp 



(frondosa) Mexicana ... 



Modiola capax 



?Rare 



Not uncommon 



Ostrea conchaphila & plumula 

 Bulla nebulosa 



Typical 



Typical, very abundant 

 Typical, very abundant 

 Typical, local 



Acmaea patina 



persona 



scabra 



Very rare 





Dwarf var., common... 

 Extremely rare 



Crepidula aculeata 



Hipponyx Grayanus 



1 SD 



Petaloconchus macrophragma 

 Natica maroccana 



? Var. Calif ornica 





In this list nos. 3, 4, 8 & 16 are doubtful. Nos. 9, 10 & 11 appear to be 

 stragglers. Nos. 1, 2, 6, 7 & 13 honestly belong to both faunas, and are forms 

 of wide geographical extent; the few remaining being creatures of sedentary 

 habits, that are easily transported from place to place. Out of the 694 

 species therefore, sent from Mazatlan, to say nothing of the additional species 

 brought by Lieut. Shipley and others, only 16 are in common with Mr. 

 Nuttall's Californians ; and even these, to a very limited extent. 



79. The following table will give an abstract of what is now known of the 

 Mexico-Peruvian fauna, grouped in families and in columns according to their 

 1856. 2 a 



