eigenmann: the cheirodontin^. 27 



Origin of dorsal equidistant from tip of snout and base of middle caudal rays 

 or a little nearer the latter; dorsal truncate, tip of third to seventh ray about equal 

 when the fin is half closed; highest ray a little shorter than head; adipose fin small, 

 but well developed; caudal lobes about equal to length of head; origin of anal 

 under end of dorsal, last twelve rays of anal of about the same height, the third to 

 eighth forming a lobe two and a half times as high as the posterior rays, very 

 little longer than snout and eye ; ventrals not reaching anal by three or four scales, 

 their origin far in advance of the dorsal; pectorals not reaching ventrals by two to 

 three scales. 



Scales everywhere very regularly imbricate, pores developed on seven to 

 fourteen scales and on the last scale of the series above the lateral line series, a 

 long tube on the base of the middle caudal ray; sheath of scales covering the 

 basal fifth of the caudal lobes, the last scale on each lobe largest ; anal with not over 

 four scales forming a sheath for the anterior rays ; axillary scale large ; scales usually 

 with two sub-parallel radials, the circuli on at least the basal part of the exposed 

 portion of the scale prominent above and below. 



A diffuse, but quite evident, shoulder-spot; margin of caudal dusky, a silvery 

 lateral band; first dorsal ray dark, a few chromatophores on the membranes from 

 the middle of the first to the tip of the penultimate, forming a very faint, oblique 

 band; bases of some of the rays dusky. 



Male with hooks on the third to the eighth anal ray; i. e., on the anal lobe, 

 which is equal to the snout and eye. 



This is the largest species of the genus and is abundant in the Paraguay to 

 San Luiz de Caceres. 



5. Aphyocharax alburnus (Glinther). 



Chirodon alburnus Glinther,^' Proc. Zool. Soc. London, 1869, p. 424, fig. 2 (Peruvian 



Amazons) . 

 Aphyrocharax alburnus Eigenmann & Eigenmann, Proc. U. S. Nat. Mus., Vol. 



XIV, 1891, p. 292; Ulrey, Ann. N. Y. Acad. Sci., Vol. VIII, 1895, p. 292; 



Eigenmann, Reports Princeton Univ. Exped. Patagonia, Vol. Ill, 1910, p. 429. 



" Giinther's original description is very brief and reads: 

 "D. 10. A. 20. L. lat. 37. L. transv. 11. 



Tlie hciglit of the body is a little more tlian the length of the head, and one-fourtii of the total (without 

 caudal) . Upper profile of the head not concave. The pectoral does not extend to the ventral. Teeth scarcely 

 compressed, pointed, with a minute (microscopical) lobe on each side; there are about twelve in the upper and 

 eighteen in the lower jaw. Sides with an ill-defined silvery longitudinal band; the middle caudal rays blackish. 



Two and a half inches long." 



