Jordan and Evermann. Fishes of North America. 345 



of them are specially modified. The tail is isocercal ; that is, with the 

 caudal vertebrae remaining in a straight line to its extremity, as in the 

 embryos of most fish, and in the Anacanthini. 



We begin our discussion of the eels with the forms which seem nearest to 

 the primitive stock from which the members of the group have descended. 

 It is evident that among the eels, the forms of simplest structure, as Uro- 

 pterygius, Channomunma, and Sphagebranchus are not in any sense primitive 

 forms, but the results of a long continued and progressive degeneration, 

 so far as the fins and mouth parts are concerned. The Apodes are proba- 

 bly descended from Isospondylous or Iniomous types, possibly from ances- 

 tors of the Anacanthini, and their divergence from typical forms is, in 

 most respects, a retrogression.* (a, without ; irovs, foot, from the absence 

 of ventral fins.) 

 (Mursenidse, GUNTHER, Cat., viu, 19-145, 1870.) 



FAMILIES OF APODES. 



ENCHELYCEPHALI : 

 a. Gill openings well developed, leading to large interbranchial slits ; tongue present ; opercles 



and branchial bones well developed ; scapular arch present. 



b. Skin covered with rudimentary embedded scales, usually linear in form, arranged in 

 small groups, and placed obliquely at right angles to those of neighboring groups; 

 pectorals and vertical fins well developed, the latter confluent about the tail ; lateral 

 line present ; posterior nostril in front of eyes ; tongue with its margins free, 

 c. Gill openings well separated ; branchiostegals long, bent upwards behind. 



d. Gill openings lateral and vertical ; snout conic, the jaws not very heavy ; gape 

 longitudinal ; lips thick ; lower jaw projecting ; teeth in cardiform bands 

 on jaws and vomer ; eggs minute. ANGUILMDJE, XLIII. 



dd. Gill openings horizontal, inferior. 



e. Snout very blunt, with very strong jaws; gape transverse; lips obsolete; 



teeth blunt, in one series, on jaws only. SIMENCHELYIDJE, XLIV. 



ee. Snout conical and slender, the jaws of moderate strength ; gape lateral; 



lips obsolete ; tongue but little developed ; teeth acute, in bands on 



jaws and vomer. ILYOPHID.K, XLV. 



cc. Gill openings inferior, very close together, apparently confluent ; branchiostegal 



rays abbreviated behind ; head conical ; tongue small ; posterior nostrils in 



front of eye. SYNAPHOBHANCHJD.E, XLVI. 



bb. Scales wholly wanting ; eggs (so far as known) of moderate size, much as in ordinary 



fishes. 



/. Tip of tail with a more or less distinct fin, the dorsal and anal fins con- 

 fluent around it ; the tail sometimes ending in a long filament. 

 Coloration almost always plain, brownish, blackish, or silvery, the 

 fins often black-margined. 



g. Posterior nostril without tube, situated entirely above the upper lip. 

 h. Tongue broad, largely free anteriorly and on Bides ; vomerine 



teeth moderate. 



t. Pectoral fins well developed ; body not excessively elon- 

 gate ; lower jaw not projecting ; anterior nostril 

 remote from eye. LEPTOCEPHALID^E, XLVII. 



hh. Tongue narrow, adnate to the floor of the mouth or only the 

 tip slightly free ; vomerine teeth well developed, some- 

 times enlarged. 



j. Jaws not attenuate and recurved at tip ; gill openings 

 well separated ; antefior nostrils remote from eye. 



- *For a detailed account of the species of Apodes, see "A Preliminary Review of the Apodal 

 Fishes or Eels," Kept. U. S. Fish Comm., 1888, (first published June 14, 1892), pp. 581-677, by 

 David Starr Jordan and Bradley Moore Davis. 



