PHCEBETEIA. 
The cuts here given show the difference between the two species better 
than many words : the bill of P. 'pal'pehrata has the groove on the lower mandible 
narrow, while the bill of P. fusca has a wide mandibular groove ; in the 
former it is filled with a purple skin, in the latter an orange one. I consider 
the reduction of the groove in the former points to an intermediate stage 
between P. fusca and Thalassarche and TJialassogeron, and that the bar at the 
base of the lower mandible in Thalassogeron is the last remnant of this man- 
dibular groove skin. In juveniles of Thalassogeron the angle made suggests 
such origin, and the absolute reduction present in the two species here noted 
indicates the method of loss. 
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