SOFT-SHELLED TURTLE. 671 
Cistudo ornata, Agassiz. ' : 
Aaassiz, Cont. Nat. Hist. U. S., i, p. 445.—Cours and Yarrow, Herp. Dakota and 
_ Montana, p. 266. 
Habitat, Iowa to Upper Missouri. 
Cistudo major, Agassiz. 
Aaassiz, Cont. Nat. Hist. U.S., i, p. 445. 
Florida to Alabama. 
ORDER OPHIDIA. SERPENTS.* 
Body long and slender, serpentiform ; limbs none, but rudiments of the pelvic arch 
present in Pythons, Boas, and Tortrices; epidermal covering above in the form of 
scales, which are periodically cast off and renewed; head often with plates, under sur- 
face usually covered with scutellm; integument very extensible ; anal slit transverse ; 
eyelids wanting; tympanum none; tongue long, bifid, sheathed at base, and capable of 
protrusion ; teeth conica], not in sockets, situated upon the jaws and palate; mouth 
very dilatable owing to the presence of a quadrate bone; juga], quadrato-jugal, sternum, 
orbito-and alisphenoids absent; post-frontals, nasals, and lachrymals well developed ; 
rami of lower jaw composed of several pieces; vertebra numerous, the dorsal procmlous; 
hear t trilocular, composed of two auricles and a ventricle, the latter with a partial sep- 
tum ; lungs usually one, when two asymetrical ; urinary bladder wanting. 
* An erectile poison fang in front part of the mouth; deep pit between ihe eye and 
nostril. - : - : ‘ 5 CROTALID2. 
*A permanently erect poison fang in front part of AY lachrymal pit wanting ; 
extralimital. : : : ELAPID&. 
* No poison fang in front part of mouth j iaehee inal pit ee - COLUBRID. 
FAMILY CROTALIDA. CROTALID SNAKES. , 
Teeth in upper jaws few; erectile poison fangs in front; head usually triangular, 
plainly separable from the body; a deep pit between the eye and nostril; dorsal scales 
carinated ; urosteges undivided anteriorly ; species all venomous. 
Tail provided with arattle. a. 
Tail without rattle; cephalic plates large as in Colubride. b. 
a. Top of head covered with scales, plates if any not reaching further back than 
the eyes. : : : CROTALUS. 
a. Cephalic plates large, ae arsin ged as in Colubride. . . CROTALOPHORUS. 
b. Loral plate present. 3 - : é : < : ; ANCISTRODON. 
b. Loral plate absent. : : C : : : : : TOXICOPHIS. 
Genus CROTALUS. Linnieus., 
Cephalic region above covered with scales, a few large plates may be present anterior to 
a transverse line between the eyes; caudal ratile always present and well developed ; 
body large and strong; pupil of eye vertical; lachrymal or nasal fossa very distinct; 
rostral plate large, temporals and labials small; the two anterior inframaxillaries large. 
ee ee en ee eA We es ee 
* For plates of heads, see U. S. P. R. R. Rep., vol. x; on classification of extralimital 
N, A. species, see Baird and Girard’s Catalogue. 
