1895.} Zoology. 283 
5. The various vertebral processes increase in length and the ribs of 
the median portion of the body show a decided tendency to become 
longer, thus giving the body a spindle-shape. 
he vertebree of the body increase in number from Ancistrodon to 
Cxvialas while the caudal vertebre show a reverse tendency. In 
Ancistrodon, the ratio of the body and caudal vertebre is approxi- 
mately as 4 to 1, in Sistrurus 5 to 1, and in Crotalus 7 to 1. 
Ancistrodon Beauvois, 1799. 
Upper surface of the petrosal region convex and not unusually ex- 
tended to form a support for the squamosals. Post-orbital portion of 
the parietals without lateral expansions. Pterygoids toothed posterior 
to their junction with the ectopterygoids. Posterior ends of the ecto- 
pterygoids grooved and notched and placed in a socket formed in the 
upper surface of the pterygoids. Palatines either triangular or club- 
shaped ; in the latter case, attached to the pterygoids by their more 
expanded ends. 
Post-frontals rudimentary if present. Posterior caudal vertebre not 
coossified, i. e., end ossicle absent.’ Number of vertebre of the body 
from 140 to 154; tail 40 to 54. 
Eastern and southern United States and Mexico. 
Ancistrodon piscivorus La Cepede, 1787. 
Outer opening of the lachrymal foramen slit-like and on the anterior 
margin of the prefrontal. Palatines club-shaped and their more ex- 
panded ends attached to the pterygoids. 
Number of vertebrx of the body from 138 to 145; tail 30 to 48. 
Ancistrodon contortrix Linne, 1766. 
Outer opening of the lachrymal foramen on the anterior upper sur- 
face of the prefrontal and situated just beneath a small pointed process. 
Palatines small and triangular in outline, with the obtuse angle point- 
ing upwards. According to Peters, A. contortrix pugnux possesses a 
palatine bone equiangular in outline.‘ 
Number of vertebre of the body from 150 to 155; tail 25 to 40. 
3In the Rattlesnake, some seven or eight posterior caudal vertebre coossify, 
in the process of the growth of the animal, and the bone thus formed has been 
variously named. J. Czermak speaks of these coossified vertebree as ‘“‘ Endkorper 
der Wirbelsaule”’: see Ueber den Schallenzeugenden Apparat von Crotalus 
zeitschrift fur wiss. Zoologie. Bd., VIII, p. 294, 1857. Hoffman accepts the 
name given by Czermak : see Dr. H. G. Bronn’s Klassen und Ordnungen des 
Thier reichs. Sechster Band. III, Abtheilung. Reptilien, III, p. 1417, 1890. 
Garman calls this bone the Shaker: see On the Evolution of the Rattlesnake. 
Proc, Bos. Soc. Nat. Hist., Vol. XXIV, 1889. 
* Loc. cit., p. 673. 
