The Fishes 



OF 



NORTH AND MIDDLE AMERICA 



BY DAVID STAKK JORDAN AND BARTON WARREN EVERMANN. 



Ichthyology (Ix^'^iXj tish; '/.oyac, a discourse) is the study of fishes. A 

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

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

 cardii, Marsipohrancliii, and Pisces. The Tunicata and Entiropneusta (Balano- 

 glossHs), now recognized as belonging to the CHORDATAaud approxiuiated 

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

 dition these creatures have undergone a retrograde metamorphosis and are 

 by 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 — 

 Leptocardii, Marsipohranchii, and Fisces. 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 

 Dipnoaus 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 op the Classes op Fish-like Vertebrates. 



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

 rounded by a protective capsule, 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 line 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. Leptocardii, 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 iuto two parts. 



c. Skull imperfeetl}' developed and without jaws ; shoulder girdle and pelvis obsolete ; 



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

 cartilaginous. Marsipobuanchii, ii. 



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

 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, m. 



F.N, A. 2 (1) 



