SOUTH AMERICAN NEMATOGNATHI. 353 



dermal bone, the " arm "of the paddle being concealed 

 by other dermal plates, the expanded portion of the 

 paddle forming the plate in front of the dorsal plate. In 

 the Plecostomince they also articulate with the temporal 

 plates. The whole apparatus gives fixity to the dorsal 

 spine but prevents lateral motion of the head. A similar 

 structure is found in the Doradince. 



ANALYSIS OF THE GENERA OF LORICARIID.E. 



a. Tail long, depressed posteriorly, with a single series of plates on the 

 sides; dorsal fin inserted behind the origin of the ventrals (except in 

 Harttia), upper caudal lobe sometimes produced; no adipose fin; intes- 

 tinal canal usually not much longer than the body. (LoRiCARHN^E.) 

 b. Dorsal fin placed above the anal, 6-8 plates between the dorsal fin 

 and the occipital plate; snout long and narrow; ventral surface cov- 

 ered by two or three series of large plates; body very slender, sub- 

 cyclindrical. FARLOWELLA LXXI. 



bb. Dorsal fin inserted above or slightly behind the anal; 2-5 plates be- 

 tween the dorsal fin and the occipital plate, 

 c. Eyes superior. 



d. Tail with strong lateral keels. 



e. Snout elongate, the tip expanded and margined with recurved 



spines; body greatly depressed; head strongly striate-hispid; a 



strong curved pectoral spine. Teeth rudimentary, present in 



the lower jaw only. HEMIODONTICHTHYS LXXII. 



ee. Snout not expanded at tip nor margined with spines. 



LORICARIA LXXIII. 



dd. Tail without lateral keels; body short and broad, greatly de- 

 pressed; belly naked; teeth numerous, well developed. 



HARTTIA LXXIV. 



cc. Eyes strictly lateral, the orbit slightly infringing on the lower sur- 

 face of the head. OXYROPSIS LXXV. 

 aa. Tail short, compressed or rounded; lips entire; lower caudal lobe 

 sometimes produced; adipose fin usually present. 



e. Ventral surface covered with two or three series of rather large plates 

 (species of small size). D. I, 6 or 7; margin of snout granular, or 

 with short booklets ; preopercle without erectile spines; dorsal inserted 

 slightly before or behind the ventrals. HYPOPTOPOMIN.. 



/. Head greatly depressed; orbit infringing on its upper and lower 

 surface; snout spatulate; adipose fin present or wanting. 



HYPOPTOPOMA LXXVI. 



ff. Head moderately depressed; orbit wholly lateral. 

 g. Temporal plate normal, imperf orate. 



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