326 characinid^;. 



of scales between the lateral line and the origin of the dorsal fin. 

 In the males the pectoral extends somewhat beyond the base of the 

 ventral, whilst the females have it shorter. I have not observed, in 

 any of the other species, this sexual difference so much developed, the 

 males and females scarcely differing in this respect. 



19. Tetragonopterus petenensis. 

 D. 11. A. 27. L.lat. 37. L. transv. 7/7. 



The height of the body is one-third of the total length (without 

 caudal), the length of the head one-fourth. Snout rather compressed ; 

 interorbital space slightly convex, its width being much more than the 

 diameter of the eye, which is two-sevenths of the length of the head. 

 The upper profile of the head is scarcely concave. The maxillary 

 extends beyond the vertical from the front margin of the eye. The 

 origin of the dorsal fin is in the vertical from the base of the inner 

 ventral rays. The pectoral terminates at a short distance from the 

 ventral. Sides of the body with a silvery band, which terminates in an 

 oblong black spot, occupying the root and the middle of the caudal. 



Lake Peten. Western Ecuador. 



a-b. Four inches long. Lake Peten. From Mr. Salvin's Collection. 

 c. Four inches long. W. Ecuador. From Mr. Fraser's Collection. 



20. Tetragonopterus aeneus. 

 Giinth. Proc. Zool Soc. 1860, p. 319. 



D. 11. A. 26. V. 8. L.lat. 35. L. transv. 7/6. 



The height of the body is contained twice and a half or twice and 

 three-fourths in the total length (without caudal), the length of the 

 head four times. Snout rather compressed ; interorbital space con- 

 vex, its width being more than the diameter of the eye, which is 

 contained thrice and one-third in the length of the head. The upper 

 profile is slightly concave above the parietal region. The maxillary 

 terminates in the vertical from the front margin of the eye. The 

 dorsal fin commences behind the root of the ventrals ; the pectoral 

 extends to, or nearly to, the ventral. Body uniform deep-bronze- 

 coloured ; a brownish spot at the root of the caudal. 



Mexico. 



a-b. Types of the species. Oaxaca. Purchased of M. Salle. 



21. Tetragonopterus wappi. 

 Cuv. fy Vol. xxii. p. 153. 



D. 11. A. 28 (25, Vol.). L. lat. 34. L. transv. 7/6. 

 The height of the body is contained thrice in the total length (with- 

 out caudal), the length of the head thrice and two-thirds ; interorbital 

 space very convex, its width being much more than the diameter of 

 the eye, which is one-fourth of the length of the head, and equals the 

 distance between orbital edge and posterior margin of the prseoper- 



