634 Notes on some South American Fishes. 



There is no difiBculty in distinguishing the adult of this species 

 from the adult of fasciatus, but a large number of younger speci- 

 mens I could only separate on the greater or less development of 

 the striatiofts of the scales — a character not to be relied upon. The 

 differences between 2 females, one of fasciatus 125 mm. long, and 

 one of tacustris 116 mm. long, are precisely as figured by Liitken 

 (Velhas Flodens Fiske), figs. 13 and 15. 



fasciatus. 



Head longer than deep at tlie occiput. 



Depth 2f; head 4. 



Anal 3, 21. 



Scales of the sides with from 8 — 12 



longitudinal ridges. 

 Suborbital with strong ridges. 

 Eye 3| in head. 

 Humeral spot small, round . 



lacustris. 



Head deeper than long. 



Depth 21 ; head 4. 



Anal 3, 25. 



Scales of the sides with one or two 



longitudinal ridges. 

 Suborbital nearly smooth. 

 Eye 3 in head. 

 Humeral spot longitudinally ovate. 



These differences, striking as they are, completely disappear with 

 smaller and smaller specimens. The anal ineach species has on an 

 average 3, 22 rays, the number of rays of lacustris in the Rio 

 Grande being less than in the Rio das Yelhas. Scales between 

 lat. 1. and ventrals 4^ — 5^. 



TetragonopterUS fasciatus (Cuvier). Numerous specimens, 9 a"<l 

 ^ , 26 — 12.") mm. from Rio Grande do Sul. 



Scales 6 or 7—32 to 36—4 to 6 ; D. 10 ; A. 2 or 3, 19—2.5. Head 4 ; depth 

 2| — 3. Eye 2| — 4, equal (in young) or less (in adult) than interorbital 

 space. Profile depressed over the eye. Maxillary with one to three teeth. 

 Occipital process rather long and pointed ; 10 to 12 scales in front of the doi'sal ; 

 13 — 15 scales from lateral line to lateral line in front of the dorsal ; 11 — 14 

 behind the dorsal ; usually no distinct median dorsal series of scales. 



Sides silvery, back bluish, a circular or vertical ovate spot on the shoulder. 

 A large conspicuous spear-shaped black spot on the caudal peduncle and 

 caudal, the black median caudal rays forming the shaft of the spear. 



The specimens agree well with the forms figured by Liitken as 

 T. rivularis. 



Tetragoiioptems fasciatus Interruptus Liitken. Five specimens, 

 % and 9 > ^15 — 67 mm. long. Rio Grande do Sul. 



These specimens are probably identical with those specimens of 

 T. rivalaris mentioned by Liitken as having an interrupted lateral 

 line. In general appearance, and especially in coloration, they are 

 exact images of T. fasciatus, from the same place. There are, 



