92 Mr. O. Salvin on the Birds of the 



5. Certhiola caboti, Holbox and Cozumel. 



6. Spindalis benedicti, Cozumel. 



7. Phmiicothraupis insular is, Meco, Mugeres. 



8. Phonipara intermedia, Holbox, Cozumel. 



9. Attila cozumel®, Cozumel. 



10. Chlorostilbon forficatus, Holbox, Mugeres, Cozumel. 



11. Centurus canescens, Ruatan. 



All of these are of mainland affinities, except Certhiola 

 caboti and Spindalis benedicti. 



It will be seen from the foregoing lists that the affinities 

 of the birds of these islands, as a whole, as might have been 

 expected from their position, are largely on the side of those 

 of the mainland. Still there is a West-Indian element, only 

 just to be traced in Northern Yucatan by the presence of 

 such birds as Petrochelidon fulva (not yet noticed on the 

 Yucatan islands), Zenaida amabilis, and Engyptilajamaicensis, 

 which is more strongly developed in the islands. At the same 

 time it is clear that the West-Indian birds found on them 

 are either specifically identical or so closely related as to be 

 separable only by some slight modification of colour. 



These differences being so slight, it is hardly possible that 

 the West-Indian element in these islands can be due to any 

 ancient land-connexion with the West Indies. For, from 

 Prof. Agassiz's contour map of the Caribbean Sea ("Three 

 Cruises of the ' Blake/ " i. p. 98, fig. 57), it will be seen that 

 the whole of Northern Yucatan and the islands adjoining 

 are separated from Cuba by a depth of over 1000 fathoms, 

 and the Bay Islands from Jamaica by over 500 fathoms, and 

 that all the islands themselves lie within the 100-fathom line 

 of the mainland coast. If there had been any recent land- 

 connexion, a supposition which the similarity of the birds 

 alone would justify, the mainland, as well as the West 

 Indies, would hardly fail to show such a connexion in a much 

 more pronounced manner, and we should find, not the 

 strong contrast that exists between the faunas of Cuba and 

 Jamaica and the mainland, but a large number of features 

 in common. 



The alternative supposition to account for the West-Indian 



