MONOGRAPH OF THE PETRELS. 



b'. Throat, flanks and under wing-coverts grey, as 



also the fore-neck and sides of neck . . . . exsul, p. 304 



b. Larger ; wing, 5.35-5.75 inches ; bill and feet very- 

 large and heavy . . . . . . . . . . garnoti, p. 307 



FAMILY IV.— DIOMEDEID.E. 

 (Salvin, Cat. Birds Brit. Mus., XXV., p. 440, 1896.) 



Key to the Genera. 



a. With no longitudinal groove on the under mandible ; 



tail short and rounded. 



a'. Base of the culminicorn wide, joining the 



proximal end of the dorsal edge of the latericorn Diomedea 



b' . Base of the culminicorn narrower, divided by 



a membrane from the latericorn . . . . . . Thalassogeron 



b. With a longitudinal groove on the under mandible ; 



tail long, wedge-shaped . . . . . . . . Phcebetria 



The above characters are taken from Salvin's " Catalogue," but I have 

 examined several species of Thalassogeron and Diomedea, which were almost 

 inseparable generically. Mr. Pycraft, however, has found some osteological 

 characters which he considers to be sufficient for their separation. He sends me the 

 following note on the subject : — 



" Thalassogeron may be readily distinguished from Diomedea, in so far as cranial 

 characters are concerned, in the much greater width of the interorbital region of the 

 frontals, and in the greater width of the palatine ends of the pterygoids. 



" These characters sharply define Thalassogeron from Diomedea, but Diomedea 

 melanophrys presents in all other respects an extremely close resemblance to 

 Thalassogeron, so much so as to make it probable that this species has been wrongly 

 placed in the genus Diomedea. Like Thalassogeron, it presents a peculiarly inflated 

 lachrymse, and this seems to be met with in no other member of the genus Diomedea. 

 If D. melanophrys were removed from Diomedea, then that genus would be very 

 sharply defined indeed from Thalassogeron. But they are still separable on account 

 of the characters given above." 



LII 



