74 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY — IV. 



aa. Arterial bulb 'svitli a i^air of ox)posite valves ; optic nerves not forming a cbiasma. 



(Series Teleostei/) 

 c. Air-bladder (if present) connected by an air-duct with the stomach or 

 oesophagus ; ventral tins (if present) abdominal, their basilar segments 

 rudimental, usually without spines ; parietal bones usually united. 



Physostomi. 

 cc. Air-bladder without duct ; ventral fins (if present) usually thoracic or 

 jugular, without basilar segments ; spines usually present, at least in the 

 dorsal and ventral fins ; j)arietal bones sejjarated by the supraoccipital. 



Physoclisti. 



AETIFICIAL KEY TO THE FAMILIES OF PISCES. 



The following key is intended simply to facilitate the identification of 

 species^ Ko attempt is made to indicate the natural characters or rela- 

 tions of the families, and only those species of any group which occur 

 within the limits of the United States are taken into consideration. 



I.— VENTRAL FINS PRESENT, ABDOMINAL. 



* Dorsal fins 2, the anterior chiefly of soft rays, the posterior adipose. 

 A. Body naked. 

 B. Head with 4 to 8 long barbels ; dorsal and pectoral fins each with a spine. 



SlLURID^, 29, 

 BB. Head without barbels ; fins without spines. 



C. Teeth strong ; dorsal fin many-rayed Alepidosaurid^, 40. 



CC. Teeth minute ; dorsal fin short Sterxoptychid^, 43. 



AA. Body scaly. 



D. Teeth broad, incisor-like Characinid^s, 32. 



DD. Teeth (if present) pointed. 

 E. Margin of upper jaw formed by the iiremaxillaries alone. 

 r. Dorsal fin nearly median. 



G. Body with phosphorescent spots ScoPELiDiE, 42. 



GG. Body without phosphorescent spots. 



H. Head scaly ; scales cycloid ; teeth cardiform Scopelid^, 42. 



HH. Head naked; scales ctenoid ; teeth villiform.-PERCOPSiDiE, 47. 

 FF. Dorsal fin posterior j teeth unequal ; body elongate . . PAKAXEPiDiE,41. 

 EE, Margin of upper jaw formed by maxillaries posteriorly. 

 J. Body with phosphorescent sj)ots ; gill-rakers none. 



Chauliodontid^, 44. 

 JJ. Body without phosphorescent sjtots ; gill-rakers present. 



Salmoxid^, 46. 

 ** Dorsal fin single, preceded by free spines. 



K. Body scaleless, naked or with bony plates. 



L. Ventral fins I, 1, the spine strong ; snout moderate. 



Gasterosteid^, 64. 

 LL. Ventral fins I, 5, the spine slender ; snout prolonged. 



AULORHYNCHID^, 63. 



KK. Body scaly ; snout tubular Aulostom atid^, 62. 



* Ttvleof, perfect j bariov, bone. 



