SOFT-SHELLED TUETLE. 671 



Cistudo ornata, Agassi z. 



Agassiz, Cont. Nat. Hist. U. 8., i, p. 445.— Cotjes and Yarrow, Herp. Dakota and 



Montana, p. 2@6. 

 Habitat, Iowa to Upper Missonri. 



Cisiudo major, Agassi z. 

 Agassiz, Cont. Nat. Hist. U. S., i, p. 445. 

 Florida to Alabama. 



ORDER OPHIDIA. SERPENTS.* 



Body long and slender, serpentiform ; litDbs none, but rudiments of the pelvic arch 

 present in Pythons, Boas, and Tortrioes ; 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 sontellse ; integument very extensible ; anal slit transverse ; 

 eyelids wanting ; tympanum none ; tongue long, biiid, sheathed at base, and capable of 

 protrusion; teeth conical, not in sockets, situated upon the jaws and palate; mouth 

 very dilatable owing to the presence of a quadrate bone ; jugal, quadrato-jugal, sternum, 

 orbito-and alisphenoids absent ; post-frontals, nasals, and lachrymals well developed ; 

 ramiof lower jaw composed of several pieces; vertebraa numerous, the dorsal procoolous; 

 hear t trilooular, composed of two auricles and a ventricle, the latter with a partial sep- 

 tum ; lungs usually one, when two asymetrioal ; urinary bladder wanting. 



* An erectile poison fang in front part of the mouth ; deep pit between fho eye and 



nostril. ........ CROTALlDiE. 



* A permanently erect poison fang in front part of mouth ; lachrymal pit wanting ; 



extralimital. . . . . ... ELAPiDiE. 



* No poison fang in front part of month ; lachrymal pit wanting. . CoLUBRiDiE. 



FAMILY CROTALIDiE. CROTALID SNAKES. 



Teeth in upper jiws few; erectile poison fanga in front ; head usually triangular, 

 plainly separable from the body ; a deep pit between the eye and nostril ; dorsal scales 

 carinated ; nrosteges undivided anteriorly ; species all venomous. 

 Tail provided with a rattle, a. 

 Tail without rattle; cephalic plates large as in Colutridce. t>. 



a. Top of head covered with scales, plates if any not reaching further back than 

 the eyes. ....... Ckotalus. 



a. Cephalic plates large, and arranged as in ColuhridcB. . . Crotalophorus. 



b. Loral plate present Ancistrodon. 



6. Loral plate absent. ... . . ... Toxicophis. 



Gbnus CEOTALUS. LinnsBus. 



CepTialie regio^i above covered witTi scales, a few large plates may be present anterior to 

 a transverse line between the eyes; caudal rattle always present anA well developed; 

 body large and strong ; pupil of eye vertical ; lachrymal or nasal fossa very distinct ; 

 rostral plate large, temporals and It^ials small ; the two anterior inframaxillaries large. 



*For plates of heads, see U. S. P. E. E. Eep., vol. x; on classification of extralimital 

 N. A. species, see Baird and Girard's Catalogue. 



