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1894.] The Classification of Snakes. 837 
relation is more pronounced than in other. In the Colubroidea 
the right or ventral lung is generally present, but of very 
much reduced proportions, the usual size being from two to 
five millimeters in length (Plate XXVIII RL). Itis connected 
with the other lung by a foramen which perforates the tracheal 
cartilage at a point a little beyond the apex of the heart, and 
opposite to the proximal part of the dorsal lung. It is some- 
times connected to the dorsal lung by a short tube, in which 
cartilaginous half rings are seen in but two of the genera ex- 
amined, viz., Heterodon and Conophis. The lumen of the 
rudimental lung may be lined by the same reticulate structure 
as is seen in the dorsal lung, or its walls may be smooth. In 
some Colubroidea the rudimental lung is absent, but such 
species are relatively few. 
The dorsal lung may present proximally alongside of the 
trachea an auricle or pocket, and this is so developed in the 
genus Heterodon (Plate XXVIII), as to reach to the head, with- 
out communication with the trachea, other than that furnished 
by the normal’ portion of the lung. In the Solenoglypha, 
without exception, this extension of the dorsal lung is present, 
and extends to the head, and its lumen is continuous with the 
trachea throughout its length. The same structure exists in 
the genera Hydrus and Hydrophis; and also in the West 
Indian'peropodous genus Ungualia, which differs besides from 
other Peropoda in having but one posttracheallung. Finally 
the tracheal lung, as I shall call it, is distinct from the true 
lung in the water snakes Platurus and in Chersydrus. In the 
former of these genera the trachea is not separate from the 
lumen, while in Chersydrus it is distinct. It, however, com- 
municates with the cells of which the lung consists in this 
genus by a series of regularly placed foramina on each side. 
There is no lumen in the tracheal lung of Chersydrus. In the 
blind burrowing Typhlops we have a still further modifica- 
tion of the tracheal lung. It is without lumen, and is com- 
posed of coarse cells of different sizes. These have no com- 
munication with the trachea or lung that I can discover. It 
. has occurred to me that this structure, which extends from the 
heart to the throat, may not be a pulmonary organ. 
