Bulletin 47, United States National Museum. 



Order X. HAPLOMI.* 

 (THE PIKE-LIKE FISHES.) 



Soft-rayed fishes with the mesocoracoid wanting, the coracoids nor- 

 mally developed, and the post-temporal normally attached to the cra- 

 nium. Parietal bones separated by the supraoccipital. Symplectie pres- 

 ent. Opercular bones well developed. Anterior vertebrae unmodified. 

 Scapular arch joined to the cranium by a post-temporal. Hypocoracoid 

 and hypercoracoid separate, with developed actinosts. Pharyngeal bones 

 distinct, the superior directed forward, 3 or 4 in number, the inferior 

 not falciform. No interclavicles. Mouth with teeth. Air bladder with 

 a distinct duct. Ventral fins abdominal, rarely wanting ; pectoral fins 

 placed low ; dorsal fin more or less posterior, the first ray occasionally 

 stiffened and spine-like 5 no adipose fin. Head usually covered with 

 cycloid scales like those on the body. Species chiefly inhabiting fresh 

 water. This order is, in some regards, intermediate between the Isospon- 

 dyli and the Acanthopteri. Part of its species, at least, are remnants of a 

 more ancient fauna than now inhabits the same waters. (u7r/l6of, simple ; 

 oyzof, shoulder, in allusion to the want of the mesocoracoid, in which 

 respect these fishes resemble the more specialized spiny-rayed forms, 

 rather than the other soft-rayed fishes.) (Physostomi, part (families Eso- 

 tidce, Unibridce, Cyprinodontidcv, and Heteropygii), Giinther, Cat., vi, vn.) 



a. Lateral margin of upper jaw formed by the maxillaries; premaxillaries not protractile; 

 vent normal. 



b. Teeth villiform, equal; jaws not produced. UMBRID^;, xc. 

 bb. Teeth cardiform, unequal; jaws depressed and produced; basis of cranium double. 



LuciiDas, xci. 

 aa. Lateral margin of upper jaw formed by the premaxillaries; basis of cranium simple. 



c. Vent normal, abdominal; premaxillaries extremely protractile. 



PffiCILIID^E, XC1I. 



cc. Vent close behind the isthmus; premaxillaries little protractile. 



AMBLYOPSID.E, xcm. 



Family XC. UMBRID^. 

 (THE MUD MINNOWS.) 



Body oblong, broad anteriorly, compressed behind. Head large, flat- 

 tened above. Mouth moderate, with bands of villiform or cardiform 



* In Dr. Gill's latest arrangement, the groups or orders here called Haplomi, SynenlognalM, and 

 Acanthopteri (exclusive of Plectognalhi) are united to form the order Teleocephali. As thus limited 

 the order would include those typical fishes in which the mesocoracoid is absent, and which do 

 not show the special peculiarities of the Pcdiculati and the Plectognathi. In earlier papers of Dr. 

 Gill the Isospondyli (Malacopteri) and the Ostariophysi are likewise included. The removal of the 

 Ostariophysi is doubtless a step in advance, but the distinctions between the Isospondyli and the 

 Iniomi and Haplorni are not of the most profound character, nor are the Plectognathi fundamen- 

 tally different from the Acanthopteri. There seems to us no special advantage in the retention of 

 a central order Teleocephali, from which the divergent branches are separated as distinct orders. 



While our knowledge of the osteology and embryology of most of the families of fishes is 

 very incomplete, it is evident that the relationships of the groups can not be shown in any linear 

 series, or by any conceivable arrangement of orders and suborders. The living teleost fishes 

 have sprung from many lines of descent, their relationships are extremely diverse, and their 

 differences are of every .possible degree of value. The ordinary schemes have magnified the 

 value of a few common characters, at the same time neglecting other differences of equal value. 

 No system of arrangement which throws these fishes into large groups can ever be definite or 

 permanent. 



