No. 586] 



///A COAL MtiASC litis AMPHIBIA 



641 



eipal with sometimes lateral and median jugular plates situated be- 

 tween the rami of the mamhblos; caudal tin diphycereal or hetero- 

 eereal; scales cycloid or rhomboid, smooth or sculptured. 



These characters may be supplemented by the follow- 

 ing: Notochord persistent or vertebras slightly ossified, 

 infraclavicle present. Teeth dendritic in a few forms. 



The following list contains brief statements concerning 

 the structures in these two groups which are usually re- 

 garded as of great taxonomic importance in all vertebrates. 



4. Comparative Table of Structures in Amphibia and 



I. Typically quadrupedal \ 

 and pentadactyl, aquatic or terres- scaled, fishes with dorsal, ventral 

 trial vertebrates. Body usually and caudal fins, 

 provided with ventral armor of Dentine of the teeth dendritic 

 ossified, calcified or chondrified in a few forms, 

 myocommata, present in modern Vertebra; usually unossified or 

 species as strands of connective incompletely. Notochord largely 

 tissue. Body completely scaled in persistent and but slightly con- 

 one species. Scales present in stricted. 



other species but incompletely Skull covered by dermal bones 



knoAvn. which are seldom sculptured al- 



IT. Teeth labyrinthine in some though possessing a similar type 



species. of lateral line system contained 



ITT. Vertebra' always ossified, within the skin, 



sometimes highly developed; as- Lateral line canals not always 



sinning various forms. Notochord impressions in bones, but similar 



incompletely persistent as inter- in arrangement to the Amphibia, 



central masses. Parasphenoid largely developed. 



IV. Skull covered with dermal The following elements absent 

 bones, which are at times variously in Amphibia but present in the 

 sculptured and grooved by pits Crossopterygia : Supratemporal os- 

 and canals. sides, ethmoid, hyomandibular, 



V. Lateral line canals present jugular plates, opercular appara- 



veloped. least one genus. 



VTL The following cranial ele- Air bladder present, with at 



ments correlated with those of the times calcified walls. 



Crossopterygia : Supraoccipital, Pelvic girdle composed of rhom- 



cpiotic. parietal, frontal, prefron- boid plate of two parts which may 



tal, nasal, premaxilla, maxilla, correspond to the ilia. 



