Classification of the Order Ostariophysi. 23 



Strong anterior canines; lateral teeth com- 

 pressed, pointed, backwardly directed, 

 uni- or bicuspid, uniserial, witli or with- 

 out minute inner teeth ; praeuiaxillary 

 decurved posteriorly, excluding the max- 

 illary from the gape Ichthyohorus, Mesoborus, 



Neoborus. 



Division 2. Gymnotiformes*. 



These Neotropical fishes differ from the Characiformes 

 externally in the short prfficaudai region and anterior vent, 

 long tapering tail, with tiie anal fin much extended and the 

 caudal reduced or absent, absence ot" dorsal and pelvic fins, 

 and restricted gill-openings. The mouth is non-prctractile 

 and the maxillaries enter the gape. In cranial osteology the 

 Gymnotiformes closely resemble the Characida3, but the 

 opisthotic is absent ; palatine and pterygoid bones are absent, 

 but the other members of the hyopalatine series are well 

 developed (PL II. fig. 3), and tlie mesopterygoid forms an 

 extensive union with the parasphenoid and vomer. The 

 suboperculum is reduced or absent. The post-temporal is 

 simple ; the coracoids show considerable differences in struc- 

 ture and development within the group. Tlie vertebral 

 column is similar to that of the Characiformes ; the centra of 

 the first four vertebrse remain distinct and the anterior ribs 

 are inserted on autogenous parapophyses. Tlie anterior and 

 posterior divisions of the air-bladder are connected by a 

 narrow duct f. 



The principal characters of the families and subfamilies 

 are shown in the following synopsis : — 



I. Maxillaries well developed, larger than praemaxillaries. Hypo- 

 coracoid >-shaped, the slender lower fork running downwards 

 and forwards to the cleithrum ; pectoral radials 4. Anterior 

 nostril superior ; vent below the head ; mouth usually small ; 

 dentition varied. Body scaly, compressed ; no electric organs ; 

 orbitosphenoid and alispheuoids well developed. 



A. Mesocoracoid well developed ; lower limb of hypocoracoid meet- 

 ing cleithrum near the symphysis ; anterior part of air-bladder 

 enclosed in a bony capsule ; mouth toothless ; maxillary articu- 

 lated with distal end of prsemaxillary ; no caudal ; no adipose 

 tin 1. Rhamjjhichthyidce. 



* Eigenmann and Ward, Proc. Washington Acad. vii. 1905, p. 159, 

 give a systematic account uf the genera and species. 

 t Ivcinhardt, Arch. f. Naturg. 1854, p. 159. 



