1508 "IHE Zoologist — January^ 1869. 



immaturity ; our best ornithologists have not corrected it, if wrong, to 

 the present day. Query. — May not those specimens of C. arcticus, 

 which are similar in plumage to the adult northern diver in winter plu- 

 mage, be adult blacktliroated divers (lesser imbers) in winter plumage, 

 and not, as supposed, young birds ? As I said, our common black- 

 throated diver is so similar in its immaturity to the redthroated diver 

 Jhat it requires an experienced eye (and even then with hesitation) 

 to discriminate between them, for both birds have the two diver- 

 gent white spots at the tip of each feather of the dorsal surface : 

 in bill they scarcely differ, the length and proportion being about 

 similar. Generally the redthroated diver has the under surface 

 of the lower mandible levelled, as it were, off and upwards, giving 

 the bill the appearance of being recurved, though the upper man- 

 dible is straight or almost so : invariably the blackthroated diver, 

 similima septeutriovdiis, has the under mandible straight, and 

 has no recurved appearance, very similar in cases to that of the 

 great crested grebe. Unfortunately this cannot distinguish it from 

 the redthroated diver in all cases. I have one of these black- 

 throated divers in my collection that has the speckled back, and 

 the black throat imperfectly assumed. Had the bird lived 1 should 

 imagine it would have been similar in a few weeks to the red- 

 throat in breeding plumage, but that the triangular patch on the 

 throat would be black instead of chestnut. Some writers have 

 believed that C. arcticus was the male of C. septentrionalis. Now 

 why so ? Surely no one could confuse the very distinct nuptial garb 

 of .C. arcticus with the totally different nuptial garb of C. septen- 

 trionalis. May they not have found the diver I allude to similar to 

 the redthroat, but having a black instead of a chestnut patch on the 

 throat? If I cannot claim a species I can, I think, claim precedence 

 in publishing that the blackthroated diver proper (if it be so) is 

 similar in its immature plumages to the redthroated diver, in so far 

 as the back is speckled similarly to that bird, and not after the type 

 of the great northern diver. Blackthroated divers may therefore occur 

 in many cases, and be mistaken for redthroats. But should it be 

 clearly known (I am deficient except in borrowed knowledge) that the 

 immature plumage of the blackthroated diver is similar to the imma- 

 ture plumage of the great northern diver, I think I have strong 

 grounds for introducing the bird as an obscure species. Any adult 

 blackthroated divers that I have seen have had the bill much larger, 

 stronger and more northern-diver shaped than the largest redthroated 



