840 PROCEEDTXas OF THE NATIONAL MUSEUM. voi..xxiii. 



is isocercal — that is. with the caiKhil vortobra' rcmaiiiino- jn a straight 

 line to its cxtreiuity, as in the enibrvos of most tish, and in the 

 Anacant/tai/. 



We begin our discussion of the eels with the forms vvhicii seem near -I 

 est to the ])rimitive stock fi-om which the members of the oi-oup iiavej 

 descended. It Is evident that among- the eels the forms of simplest 

 structure, SpJiagrhrdncJnii'i^ etc., are not in an}' sense primitive^ forms, 

 l)ut th(^ results of long-continued and progressive degeneration, so far 

 as the fins and mouth parts are concerned. The A2)odes are probably ] 

 descended from soft-rayed fishes, and their divergence from typical 

 forms is, in most respects, a retrogression. («'-withoLit; Trovg, foot, 

 from the absence of ventral tins.) 



FAMILIES OF APODES. 



a. EnclichicephaU : Gill openin<i;s well (level()i)e(l, leading to large interbraiirhial slits; 

 tongue ])rest'nt; ()])er('leH and hranchial lionew well develoi)ed; sca|mlar arch 

 present. 

 /;. Skin covered with rudinientarj' emhcddcd scales, usually linear in form, 

 arranged in small groups, and placed olirKiudy at right angles to those of 

 neighboring groups; ])ectorals and vertical lins well developed, tlie latter con- 

 tinent about the tail; lateral line present; pusterior nostril in front of eyes; 

 tongue with its margins free. 

 c. Gill openings well se|)arated; brancliiostegals long, bent u]i\\ards behind. 

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

 gape longitudinal; lips thick; lower jaw i)rojecting; teeth in cardiform 



bands on jaws and vomer; eggs minute Anguillid.e. II. 



fc. (Jill oi)enings inferior, very close together, ap))arently confluent; branchios- 

 tegal rays abbreviated behind; head conical; tongue small; posterior nos- 

 trils in front of eye Svn.aphobranciiid.k. III. 



hli. Scales wholly wanting; eggs, so far as known, (tf moderate size, much as in 

 ordinary lishes. 



(. Tail not mncli if any shorter than rest of bod>-; heart placed close behind 

 the gills. 

 /. Tip of tail with a mtjre or less distinct lin, the dorsal and anal lins con- 

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

 ation almost always plain, brownish, blackish, or silvery, the fins 

 often black-margined. 

 (J. Posterior nostril without tube, situated entirely al)Ove the upper lip. 

 //. Tongue broad, largely free anteriorly and on sides; vomerine teeth 

 moderate. 

 I. Pectoral fins well developed; body not excessively elongate; 

 lower jaw not i)r()jt'cting; anterior nostril I'emote from eye. 



LKeTOCKlMIALID.K. IV. 



////. Tongue narrow, adnate to the floor of the month or only the 

 til) slightly free; vomerine teeth well developed, sometimes 

 enlarged. 

 j. .laws not attenuate and recurved at tip; gill o})enings well sepa- 

 rated; anterior nostril remote from eye. 

 k. Pectoral fins well developed; skin thick; skeleton firm; 

 snout moderate; tail not ending in a filiform tip. 



MuR-ENESOCinji:. V. 



