550 THE AMERICAN NATURALIST. [Vor. XXXV. 
character among the Alca. In some sterna a small foramen 
may occur upon one side only, and even this may be absent. 
Between these extremes a great variety of patterns is to be 
met with, as a notch upon one side and a foramen on the 
other, or both foramen and notch upon either side. The 
sternal body is long and narrow in Alca, Uria, Synthlibo- 
rhamphus, Brachyrhamphus, and in the extinct Plautus, — those 
species, on the other hand, in which the sternum has a single 
notch on either side, and a single foramen within its inner 
border, the sternal body is rather broader anteriorly and 
more spreading behind, as in Cepphus, Lunda, and Fratercula. 
In Simorhynchus the sternum, having the same fundamental 
pattern, is long and narrow, with the xiphoidai extremity much 
produced beyond the carinal termination, being swelled and 
concave above and with one large, oblique, elliptical foramen 
on either side. This character also varies for different genera 
and species. The skeletons of the limbs do not appear to offer 
any constant characters. Full descriptions of the morphology 
of these parts, as well as the various forms of the sternum, are 
given in my previous memoirs, and they are illustrated by 
numerous cuts and figures, both in the text and on the 
plates. 
On the Systematic Position of the Alce. 
The Alcz constitute a suborder of birds, in which is included 
but the single family Alcida. This family may be conven- 
iently divided into two subfamilies, — the Alcinæ, containing 
all the true auks, and the Fraterculinz, containing the puffins. 
As a group the Alca are connected upon the one hand with 
the Limicola through the Longipennes ; in other words, to the 
great snipe-plover group, and their allies through the gulls and 
their allies. On the other hand, they are connected with the 
Pygopodes and Impennes through the Tubinares, that is, 
through the petrel types with the penguins, the loons, the 
grebes, and their extinct allies, the toothed birds of the hesp 
rornithine type of structure. Later on these relationships will 
be set forth in my scheme of classification of the class Av 
now in the course of completion. 
