526 JNIr. P. II. Lowe — Observatiuas 



groups of islands just mentioned, no normally coloured 

 forms have as yet been met with. 



As regards local conditions as a predisposing cause, it is 

 only necessary to mention the totally different geological 

 and other conditions obtaining in St, Vincent and Grenada 

 as compared with those on the Venezuelan Islands. 



Prof. Bateson informs me that he is of opinion " that it 

 is scarcely possible that the difference (between the two 

 forms) is brought about by loss of any factor already 

 possessed by the type and that the black form differs 

 from the normal in possessing one factor more. As to 

 how a new factor comes to be added there is no evidence 

 whatever." 



Prof. Bateson goes on to add : — '•' The further difficulty 

 remains, that in view of the extreme isolation of the 

 colonies — proved by the fact that almost every island (in 

 the West Indies) has its own type — we are driven to suppose 

 that the assumption of the factor of black has independently 

 come to pass on St. Vincent, Grenada, the Testigos, and 

 Los Roques. This is a very serious difficulty ; but I think 

 it must be faced, for if a black form could have in any way 

 travelled from the place of first origin, then such inter- 

 communication between the islands luust be supposed to be 

 not very difficult ; for at least four localities are affected. 

 This would be incompatible with the development of such 

 definite island forms and especially with the absence of 

 black phases on the Grenadines." 



CCEREBA WELLSI. 



Certhiola welld Cory, Auk, vi. 1889, p. 219 (Grenada, 

 Lesser Antilles; Coll. C. B. Cory). 



Caereba ivellsi Ridgw. Birds N. & M. Amer. pt. ii. 1902, 

 p. 423. 



Coereba ivellsi (Black form) Austin Clarke, Auk^ xxii. 

 p. 393. 



Hab. Island of Grenada, Lesser Antilles. 



Measurements. Wings oi 7 S S average from 59-61 mm. 

 Bills average smaller than in C. alrata. 



