236 The American Naturalist. [March, 
and he places his Lariformes between his Alciformes and 
Charadriiformes. (p. 72.) 
My own cabinet contains numerous skeletons of Longipen- 
nine birds, and, thanks to the U. S. National Museum, I have 
had the opportunity of examining very many more. 
Recently I have gone thoroughly over this material and 
written out full descriptions of the characters presented on : 
the part of our American Longipennes, and chiefly from 
osteological data it would seem to me that the following classi- 
fications can be sustained as being probably the most natural 
one. 
SUB-ORDER. FAMILIES. SUB-FAMILIES. 
f LARIDÆ. / Leine. 
Sterninæ 
LONGIPENNES. 1 STERCORARIIDA. 
i RHYNCHOPIDÆ. 
So far as our American Laridæ are concerned, and it is fair 
to presume that the fact obtains elsewhere in the world, we 
observe that certain genera among the Gulls almost insensibly 
approach in their structure and merge into certain genera of 
Terns. Xema sabinii is closely related to such a species as 
Sterna paradisea, while Gelochelidon comes near some of the 
heavier built Larinz. 
Iam of the opinion that the Skuas and Jaegers (Stercora- 
riidx, stand between the Laridæ and the Rhynchopidz, being 
more nearly related to the first named than they are to the 
Skimmers. Indeed it would seem that the family Rhynchop- 
idx is more remotely related to either of the other two 
families of the Longipennes, than has heretofore generally 
been supposed. Rhynchops I have shown in a memoir that I 
have sent to the Journal of Anatomy (Lond.) for publication, 
is, in some of its osteological characters notably in the skull, 
the vetebral chain, and pelvis, not very unlike the fossil 
cretaceous bird Ichthyornis, and this is a very remarkable 
fact. 
Through the Laride of the present SUB ORDER, the Longi- 
pennes are found to be not so very distantly connected with the 
Alex, the genus Uria among the Auks standing between 
certain Gulls and the more ancient types, such as Plautus and 
