22 THE ROYAL SOCIETY OF CANADA 



Platysomus canadensis differs from all other described species 

 of the genus in its general proportions, as well as in details of struc- 

 ture. Its great size, far surpassing that of any known member of the 

 family, and the basal length of the dorsal and anal fins are note- 

 worthy. Its general outline is somewhat like that of the relatively 

 small P. gibbosus (Blainville) from the Upper Permian of Germany 

 and England. In both species there is a trunk-area, with small scales, 

 above the base of the anal fin. The very small North American species 

 which have been referred to this genus are from the Coal Measures 

 of Illinois (Newberry and Worthen, and Cope) and the Permian of 

 Indian Territory (Cope). The high position of the pectoral fin in 

 the type, and only known specimen of P. canadensis is also a character 

 to which attention is drawn. 



Measurements. mm. 



Length of specimen 3 feet, 83^ inches 114a 



Length from anterior end to caudal peduncle 825 



Height of specimen, including fins (vertical) 703. 



Height of specimen, excluding fins (vertical) 540 



Spread of caudal fin, approx 420 



Height of caudal peduncle 45 



Length of dorsal fin at base 525 



Depth of anterior end of dorsal fin, approx 70 



Depth of posterior end of dorsal fin 30 



Length of anal fin at base 420 



Depth of anterior end of anal fin 165 



Depth of posterior end of anal fin 23 



Height of flank-scales (figured) midway between dorsal 



angulation of body and vertebral column (approx) 43 



Breadth of same (approx.) 18 



Height of flank-scales midway between vertebral column and 



ventral angulation of body (approx.) 65 



Breadth of same (approx.) 22 



Number of articulations in fin-rays near base of anterior end 



of dorsal fin ; 8 in space of 10 



Breadth of rays at same point 2 



Number of articulations in fin-rays near base of anterior end 



of anal fin ; 6 in space of 10 



Breadth of rays at same point 3 



