THE FISHES 



OF 



NORTH AND MIDDLE AMERICA 



BY DAVID STARR JORDAN AND BARTON WARREN EVERMANN. 



Ichthyology (q;#i'f, fish; A6yof, a discourse) is the study of fishes. A 

 " fish," iii the popular sense, is a member of any one of the three classes 

 of aquatic or fish-like vertebrates, the groups here designated as Lepto- 

 at </*'/, Marsipobranchiij and Pisces. The Tunicata and Enteropneusta (Balano- 

 gl()8sus),now recognized as belonging to the CHORDATA and approximated 

 to the VERTEBRATA, are excluded in this definition, as in their adult con- 

 dition these creatures have undergone a retrograde metamorphosis and are 

 hv no means fish-like. For an opposite reason, the BATRACHIA, which de- 

 velop jointed limbs in their adult condition, although closely allied to the 

 true fishes, are not included in the popular idea of a fish. 



Among the forms commonly called fishes we recognize three classes 

 Leptooardii, Marsipobranchii, and Pisces. We have preferred to leave the 

 Pisces as a single class, including all fish-like vertebrates with paired fins, 

 though there is much to be said in favor of regarding the Selachians and 

 Dipnoans as each constituting a distinct class coordinate with the true 

 fishes and the Batrachians. We see no warrant for separating the Ganoids 

 as a class from the true fishes, still less for uniting the Ganoids and Sela- 

 chians in one class, Palceichthyes, while the true fishes are placed in another. 



ANALYSIS OF THE CL\SSES OP FISH-LIKE VERTEBRATES. 



a. Acraniata. Anterior end of the central nervous axis not dilated into a brain and not sur- 

 rounded by a protective capsu-le, or skull. 



b. Notocbord perfect, persistent, extending throughout the body, included in a membranous 



sheath, as is the cord-like nervous axis above it ; body elongate, lanceolate, not 

 worm-like nor enveloped in a tunic ; walls of the body with muscular myotomes ; 

 middle lino of body with rudimentary fins; no proboscis; the mouth slit-like, 

 fringed with cirri ; heart a longitudinal tubular vessel which gives off branchial 

 tubes which unite in an aorta ; gill slits inclosed externally by a fold in the in- 

 tegument which incloses a chamber (atrium) which opens below ; vent remote 

 from mouth. LEPTOCABDII, i. 



aa. Craniota. Anterior end of the nervous axis dilated into a brain which is contained within 



a protective capsule, the skull ; notochord not continued forward beyond the pituitary 



body ; heart developed and divided at least into two parts. 



c. Skull imperfectly developed and without jaws ; shoulder girdle and pelvis obsolete ; 



no paired fins ; a single median nostril ; gills purse-shaped ; skin naked ; skeleton 

 cartilaginous. MAHSIPOBRANCHII, n. 



cc. Skull well developed, and with jaws; shoulder girdle and pelvis more or less developed ; 

 nostrils not median ; gills not purse-shaped ; limbs, if present, developed as rayed 

 fins, never with fingers and toes like those of the higher vertebrates ; gills per- 

 sistent through life. PISCES, in. 



F. N . A. 2 (1) 



