thp: batrachia of north America. 33 



rediiced in size. In soiine families tlic pterygoids never ossily, and dis- 

 appear. An iilnstratiou of tbe late ])ersistence of the osseous pteiygo 

 palatine arch is seen in the larva of (Jliondrotus tenehrosns. (See Plate 

 24.) 



Tbe systematic arrangement of the Urodela may be represented as 

 follows : 



I. Lateral and mexliaii hyoicl elements distinct. 



A. Two pairs of ccratobraucbial bones; stapes connected witb (juadrate arch; 



no doable hypopopbyscs. Tremaiodera. 

 No first epibrancbial ; no double bypopopbyses of vertebrie; vertebrae ani- 

 pliicoelous; ceratobyal connected witli quadrate by ligament only; 

 vomeropalatine bones witb teetb on tbe anterior margin; vestibule 

 witb membranous inner wall ; no paraspbeuoid teetb. 



Crupiohrandildw. 



B. One pair of ceratobraucbial bones; stapes connected witb quadrate arcb; liypo- 



popbyscs double. AmpMumoidca. 

 No first epibrancbial, several otbers present; vertebra; ampliiccelous ; an eth- 

 moid; scapular and pelvic arches present; ceratobyal couuccted with 

 quadrate by ligament only; liver little sub divided AmpMamida>. 



C. Two pairs of ceratobrancbials; stapes not connected witb quadrate arcb in 



adult; only tbe first and rarely second epibranchials present; verte- 

 bra; without double hypopopbyses. rsnidosauria. 



1. Vertebra; ampbicoolous. 



Vomerojjalatine bones with teeth on the posterior margin ; ceratobyal 

 connected witb quadrate by cartilage ; no paraspbeuoid teeth ; vesti- 

 bule witb osseous walls; carpus and tarsus ossified; an otoglossal 

 cartilage ; no second epibrancbial elemeut Jmhiijstomidcr. 



Vomeropalatine bones with teeth on the posterior margin ; no parasphc- 

 noid teeth; no otoglossal cartilage; a second epibrancbial. 



UijuohUdw. 



Vomeropalatine bones witb teetb on the posterior margins ; paraspbeuoid 

 teeth; vestibule with osseous walls; ceratobyal connected wilii 

 quadrate by cartilage; no otoglossal cartilage; no second epibrancb- 

 ial ; carpus and tarsus cartilaginous ; no pterygoid Plethodontlia'- 



2. Vertebra; opisthocoelous. 



Vomeropalatine bones not sending processes over paraspbeuoid bone ; 

 ceratobyal connected with quadrate by cartilage ; paraspbeuoid 

 teeth; no postfrontosquamosal arch; carpus and tarsus cartilagi- 

 nous Desmognaihidw. 



Vomeropalatine bones not produced posteriorly ; paraspbeuoid teetb; no 



postfrontosquamosal arcb; carj)us and tarsus osseous Thoriida'. 



V-JUieropalatine bones extended over paraspbeuoids in" two dentigerous 

 jirocesses ; no paraspbeuoid teeth ; no osseous postfrontosquamosal 

 arch; ceratobyal only connected with quadrate by ligament | carpus 



and tarsus osseous Salamandridw. 



Vomeropalatine bones extended over parasphenoid in two deutigerous 

 processes ; no paraspbeuoid teeth ; an osseous postfroutosquamosai 

 arch; ceratobyal only connected with quadrate by ligament ; carpus 



and tarsus osseous Pleurodelidce. 



II. Hvoid elements continuous across middle line. No distinct median elements. 

 Stapes connected with quadrafe bone. Apoda. 

 Vertebme with double hypopopbyses ; an ethmoid bone j scapular and pelvic 



arches wanting ; liver greatly subdivided . . „ . , , , . , . Cccciliidce. 



1951— Bull 34 3 



