282 The American Naturalist. [March, 
Since I have undertaken a more detailed study of these snakes, I omit 
from this article extended remarks on geographical distribution and 
specific characters. Neither have I, at this stage of my work, thought 
best to adopt any system of classification’. 
I desire to make a few general statements. The upper surface of the 
skull of Crotalidae, in comparison with the skulls of other snakes, is 
quadrate in outline. The interobital region, owing to the elevation of 
the outer edges of the frontals and outer anterior angles of the parietals, 
is concave. 
The nasal bones are loosely attached. The prefrontals are quadrate 
in outline, movable, and are between the frontals and maxillaries. 
The maxillaries occupy a vertical position in front of the orbit and are 
attached above to the prefrontals and behind to the ectopterygoids. 
Each possesses a well-developed poisonous fang, and, in its outer sur- 
face, a conspicuous and characteristic pit. The parasphenoidal sur- 
face is concave and divided by a longitudinal median ridge-like process. 
Well-developed ventral processes are present on all the vertebree of the 
body. The latter never exceed 200, the combined number of body and 
caudal vertebrae not commonly reaching this number. 
Of the family Crotalidae the Ancistrodon shows the least specializa- 
tion while the highest development is found in the Crotalus. The de- 
velopment of the family is shown in the following ways: 
. By the expansion and flattening of the anterior portion of the 
skull. "This, also, takes place to a less extent in the petrosal region. 
2. By the development of the maxillary fang and consequent change 
in the position and shape of the maxillaries and prefrontals. 
3. As specialization proceeds there is a decrease in the number of teeth. 
Besides the fangs, no teeth are found on the maxillaries, and, except in 
Ancistrodon, none exist on the pterygoids posterior to their junction 
with the ectopterygoids. 
4. The freedom and mechanical arrangement of the nasals, prefront- 
als, maxillaries, palatines, pterygoids and ectopterygoids is quite nota- 
ble. 
2 In this brief article we shall not attempt to refer to the numerous authorities 
consulted However, it should be stated, perhaps, that the general osteology of 
the Crotalidae has been worked out and discussed by various naturalists. ‘The 
results of their works have appeared in many publications and under various 
dates. Also, we wish to state that Peters, as early as 1862, briefly mentions the 
craniology of the genus Ancistrodon 
Hr. W. Peters hielt einen Vortrag uber die craniologischen Verschieden- 
heiten der Grubenottern (Trigonocephali) und uber eine neue Art der Gattung 
Bothriechis. Monatsberichte der Koniglichen Preufs. Akademie der Wissen- 
schaften zu Berlin, 1862, p. 670. 
