208 



ZOOLOGY 



SECT. 



The absence of a spiral valve and of a conus arteriosus, the 

 presence of a bulbus aortae, and the decussation of the optic 

 nerves indicate its position among the Teleostei. It belongs to 

 the Physostomi in virtue of possessing a pneumatic duct, none but 

 jointed" fin-rays, and abdominal ventral fins. The characters which 

 place it among the Salmonidse are the presence of an adipose fin 

 and of pseudobranchise, the absence of oviducts, and the fact that 

 the premaxilla enters into the gape of the mouth. The genus 



B 



FIG. 832. Hippocampus (Sea-horse). In B the operculum is removed to show the gills. 

 br. up. branchial aperture ; brd. p. brood-pouch ; d. f. dorsal fin ; g. gills ; pet. f. pectoral fin. 

 (From Claus and Gunther.) 



Salmo is distinguished by its small scales, well-developed conical 

 teeth, absent on the pterygoids, a short ventral fin with fewer 

 than fourteen rays, numerous pyloric appendages, and compara- 

 tively large ova, The distinctive characters of the various species 

 of Salmo depend upon comparatively minute points, such as the 

 relative proportions of various parts, and are often difficult of 

 determination owing to individual variations correlated with 

 different environments. In S. fctrio the posterior margin of the 

 operculum is evenly curved, the maxilla is longer than the snout, 

 and the vomerine teeth are in a double series and persist throughout 

 life. 



