50 CHECK LIST OF THE 



mouths of rivers, to which they resort in late autumn. When the young 

 Eels are from two to three inches long they ascend the rivers in vast num- 

 bers, travelling continually until they meet some obstacle which cannot 

 be overcome. Professor Baird has estimated "that in the summer one 

 may see hundreds of waggon loads of young Eels at the foot of Niagara 

 Falls, crawling over the rocks and squirming in the seething waters." 

 Where the obstruction to their passage permits it, the fish will leave the 

 water and travel through wet grass in order to continue their journey. 



As a food fish Eels are justly esteemed and in the markets they always 

 sell for a high price. 



Order ISOSPONDYLI. (The Isospondylous Fishes.) 



Soft-rayed fishes with the anterior vertebra? simple, unmodified, and 

 without auditory ossicles ; symplectic present ; no interclavicles ; opercular 

 bones distinct ; pharyngeal bones simple above and below, the lower not 

 falciform. Mesocoracoid arch always well developed, forming a bridge 

 from the hypercoracoid to the hypocoracoid. Bones of jaws developed, 

 the maxillary broad, always distinct from premaxillary, and forming part 

 of margin of upper jaw; no barbels. Shoulder girdle well developed and 

 connected with the cranium by a bony post-temporal. Gills four, a slit 

 behind the fourth. Air bladder, if present, with a pneumatic duct. Dorsal 

 and anal fins without true spines. Ventral fins abdominal, sometimes 

 wanting. Scales usually cycloid, sometimes ctenoid ; occasionally wanting. 

 No developed photophores. Adipose fin pi-esent or absent. 



Familv HIODONTID.^. (The Moon-eyes.) 



Body oblong, much compressed, covered with moderate sized, bril- 

 liant, silvery, cycloid scales. Head naked, short, the snout blunt. Mouth 

 moderate, oblique terminal, the jaws about equal. Premaxillaries not pro- 

 tractile. Maxillary small, slender, without evident supplemental bone, 

 articulated to the end of the premaxillary and forming the lateral margin 

 of the upper jaw. Dentition very complete ; premaxillary and dentary 

 bones with small wide-set cardiform teeth ; maxillaries with feeble teeth ; a 

 row of strong teeth around the margin of the tongue, those in front very 

 strong canines ; between these is a band of short close-set teeth ; vomer 

 with a long double series of close-set, small teeth ; similar series on the 

 palatines, sphenoid and pterygoids; sides of lower jaw filling within the 

 upper, so that the dentaries shut against the palatines. Eye very large, 

 the adipose eyelid not much developed. Preorbital very narrow. Nostrils 

 large, those of each side close together, separated by a flap. Gill mem- 

 branes not connected, free from the isthmus, a fold of skin covering their 

 base. No gular plate. Branchiostegals eight to ten. Gill rakers few, 



