Genus — H ETEROPRION, nov. 
Small birds agreeing in general characters with species of the genus Prion, but 
differing in the shape of the bill ; whereas in that genus the lateral plates are 
widely horizontally developed, and the under-mandible rami enclose a broad 
distensible sac, in this the lateral plates are not abnormally laterally 
extended, and the rami of the under mandible are normal and no sac is 
present, the interramal space being narrow and feathered. The general 
nature of the bill is, however, similar, the nasal tubes being short, the nail 
weak and small, and the space between the nasal tubes and the nail longer 
than the former. 
Type — H. heldieri, sp. n. 
Coues introduced his genus Pseudoprion to include all the wedge-tailed 
Prions, save vittatus. He definitely named as type. Prion turtur Gould. The 
description of that species refers to the bird later known as P. ariel (=P. turtur) 
and P. brevirostris Gould, but Gould’s figure of his bird’s bill does not agree 
well with the bill of the latter species. Coues’s description of his genus seems 
more apphcable to the P. ariel {=P. turtur) group, but he also included 
P. banksi, which he afterwards admitted to be the same as P. desolatus Gmelin 
from Kerguelen. I have consequently restricted Pseudoprion to the P. ariel 
(=P. turtur) group, which I find to differ essentially from the narrow-billed 
Prions grouped about P. desolatus, and have therefore introduced the above 
genus to include the medium-billed Prions, and have named as type the 
thinnest-billed one, H. belcheri, as this shows best the great difference between 
this group and the P. ariel (=P. turtur) group. 
The species of this genus have the bill shorter and narrower, the wing 
shorter, and the tarsus shorter than the members of the genus Prion. 
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