256 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY IV. 



Order M.-ISOSPONDYLI. 



{The Isospondylous Fishes.) 



Parietals present. Symplectic present. IVo iuterclavicles. A. prsecor- 

 acoid arch. Anterior vertebrte simple. No auditory ossicles. Pharyn- 

 geal bones simple above and below, the lower not falciform. Gills 4, a 

 slit behind the fourth. A Yery large group, i^resenting many modifica- 

 tions of structure. (f<7o^, equal; ^-ovJu/oc, vertebra.) * 



{J'ht/sostomi. Giintlier, part.) 



ANALYSIS OF FAMILIES OF ISOSPONDYLI. 



* Tail diphycercal. 

 a. Lateral marj^ins of upper jaw formed by the luaxillaries. 



b. Adipose liii iioiie: no plionplioresceut spots; body usually scaly; head naked; 

 throat without barbel, 

 c. Lateral line present. 

 d. Gular plate none. 

 <'. Air-bladder none ; dorsal posterior, opposite anal and similar to it ; mouth 

 small, Avith small, pointed teeth; deep-sea fishes. 



AlepocephalidyE, 33. 



ee. Air-bladder present ; dorsal in front of anal. 



/. Mouth small, horizontal ; posterior part of tongue and the roof of the 



mouth covered with coarse, paved teeth. ..Albulid^:, 34. 



J'f. Mouth larger, oblique; teeth all pointed; those on the tongue large. 



Hyodontid.e, 35. 



dd. Gular plate present ; mouth large ; teeth all pointed Elopid^, 36. 



cc. Lateral line obsolete. 



(f. Mouth terminal, large ; maxillary iu three parts, mostly broad. 



Clupeid^, ^57. 

 f/g. Mouth small, inferior ; maxillary short and narrow ; not in three 



parts DOROSOMATID^, 38. 



(/[ig. Mouth very large, subinferior; maxillary very narrow, produced 



backward Engraulidid^, 3'J. 



bh. Adipose fin present (rarely absent, and the body with phosphorescent spots). 

 h. Throat with a long barbel ; scales very small or wanting ; mouth 



largo Stomiatid^, 4.^). 



hh. Throat without barbel. _ 

 i. Sides with phosphorescent spots; oviducts present; deep-sea 

 fishes. 



j. Pseudobranchiie none ; body scaly ChauliodontiO/E, 44. 



jj. Pseudobranchite present ; body na.ked. .Sternoptyciiid^e, 43. 

 a. Sides without phosphorescent spots; oviducts none. 



S.\LMOMl).K, 4(). 



aa. Lateral margius of upper jaw, like the anterior margin, formed by the premax- 



illaries ; adipose fin usually present. 

 k. Premaxillaries short, with villiform teeth ; mouth small ; 



bones of head cavernous ; scales ctenoid. .Percopsidj^, 47. 

 kk. Premaxillaries elongate; mouth large; bones of head not 



cavernous; scales mostly cycloid. 



I. Dorsal short, nearly median ; body scaly .. Scopelid.^3, 42. 



II. Dorsal short, posterior: body scaly.. Paralepididjl, 41. 



III. Dorsal occupying nearly the whole length of the back; 

 body naked Alepidosairid.e, 40. 



