THE AMERICAN TETRAGONOPTERINAE. 167 
22. HEMIGRAMMUS ORTHUS Durbin. 
Plate 21, fig. 1. 
Hemigrammus orthus Dursin, Ann. Carnegie mus., 1909, 6, p. 61 (Tukeit); Ercrnmann, Rept. Princeton 
univ. exped. Patagonia, 1910, 3, p. 143; Mem. Carnegie mus., 1912, 5, p. 336, pl. 48, fig. 5; Exus, 
Ann. Carnegie mus., 1911, 8, p. 163 (Santarem). 
Hasrrat.— British Guiana; Amazon. 
Specimens examined. 
Number of Size 
Catalogue number _ specimens in mm. Locality Collector 
1477 C. Type 1 28 Tukeit Eigenmann 
1478 C., 11912 I. 7 22-30 Tukeit Eigenmann 
Paratypes 
1479 C., 11922 I. 25 14-21 Gluck Island Eigenmann 
Paratypes 
1480 C. Paratype 1 27 Essequibo below Packeoo 
3600 C. 6 25-34 Hubabu Creek Ellis 
2945 C. 5 26-31 Santarem Haseman 
2948 C. 5 19-21 Konawaruk Eigenmann 
Head 3.75; depth 3.75; D. 11; A. 19 to 22; scales 5-30 to 33-3; eye 2.5 
in the head; interorbital not quite equal to the eye, about 3 in the head. 
Compressed; depth of head at the base of the occipital process about 
1.33 in the greatest depth. Preventral region rounded, without complete series 
of median scales. Predorsal region rounded, probably with a complete series 
of 9 median scales. 
Occipital process about 6 in the distance from its base to the dorsal, bor- 
dered by 2 or 3 scales on thesides. Interorbital sightly convex. Frontal fon- 
tanel triangular, narrower than the parietal and not quite equal to the parietal 
without the occipital groove. Second suborbital leaving narrow naked margins 
behind and below. Snout a little more than one half the length of the eye. 
Mouth large. - Maxillary equal to the eye, narrow, slightly curved backwards, 
the two sides parallel to each other. Mandible equal to the maxillary. Pre- 
maxillary with three tricuspid or conical teeth in the outer row, and five, 3- to 
5- or rarely 7-pointed teeth in the inner row. Maxillary with one to five tri- 
cuspid or conical teeth. Dentary with a graduated series of four or five large 
3- to 5-pointed teeth. 
Gill-rakers 7 + 14. 
