Section IV., 1914. [17] Trans. R.S.C. 



Description of a new species of Platysomus from the neighbourhood of 

 Banff, Alberta* 



By Lawrence M. Lambe. F.G.S., F.R.S.C, F.G.S.A., Vertebrate 

 Palaeontologist to the Geological Survey, Canada. 



(Read May 26, 1914.) 



An excellently preserved specimen of a species of Platysomus, 

 from rocks of presumably Permian age near Banff, Alberta, has lately 

 been received by the Geological Survey. This fossil fish was found 

 by E. W. Peyto of Banff in 1912 and was sent to the Geological Sur- 

 vey, for description, by N. B. Sanson, curator of the Banff Museum. 

 The writer wishes to express his obligations to Mr. Sanson for the 

 opportunity thus afforded of studying so fine a specimen. 



The fish is remarkable for its size, and although the head has 

 suffered from weathering and the elements composing it are not 

 distinguishable, the remainder of the specimen gives details of struc- 

 ture which largely make up for the deficiencies of the anterior part. 



As the species represented is apparently undescribed the following 

 particulars of its structure are given, and, as it is the first member 

 of the Platysomidae known from Canada, the specific name canadensis 

 is considered appropriate. 



The general shape is that of a short rhomboid ending in a deeply 

 cleft, nearly symmetrical tail. The angles of the rhomboid are the 

 highest and lowest points of the body contour, the mouth, and the 

 base of the tail. The dorsal angulation is in advance of the mid-length 

 of the body, while the ventral angulation is slightly behind it. The 

 outline from the upper and lower angulations backward to the tail 

 form two remarkably straight, converging lines. 



The trunk has a maximum height almost equal to its length 

 measured from the pectoral arch to the slender caudal pedicle. The 

 contour is perfect from the anterior end of the dorsal fin backward 

 to include the tail and forward beneath to the front end of the anal 

 fin. From the mouth to the dorsal fin the exact outline is not pre- 

 served, and between the anal fin and the mouth there is, without 

 doubt, some distortion. 



The dorsal fin, extending from the upper angulation to the base 

 of the tail, is slightly elevated in front, decreasing gradually in height 



*Communicated by permission of the Director of the Geological Survey. 

 Sec. IV, 1914—2 



