FROM THE E10 PAEAGUAY. 31 



This fish, the largest known of the genus, is possibly the adult of C. aculeatus, 

 Perugia, in which, however, the ventral region is entirely naked. 



39. Ch^etostomus cirrhosus, Val. 

 Paraguay; Descalvados, Matto Grosso. 



40. Ch^etostomus leucostictus, Gthr. 

 Descalvados, Matto Grosso. 



41. Hypoptopoma guentheri. 



Hypoptopoma guentheri, Boulengeiv, P. Z. S. 1895, p. 526. 



Head not narrowed behind the eyes, its width equal to length to posterior border of 

 orbit, its length 2f to 3 times in total ; diameter of orbit 5 to 5-| times in length of 

 head, 2-| to 2f times in length of snout, 3 to 3J times in interorbital width ; barbel 

 very small ; head-shields as in II. thoracatum. Dorsal I 6, first ray as long as head to 

 upper angle of gill-cleft. Pectoral as long as first dorsal ray, extending as far as 

 ventrals, not reaching anal. Caudal deeply notched, middle rays half as long as outer. 

 Two pairs of large transverse pectoral shields, preceded by a transverse series of four 

 small shields, the outer of which are in contact with the suborbital shields ; three or 

 four large ventral shields on each side, the anterior of which are usually separated by 

 an azygos shield. Shields on body spinulose, but not keeled, 20 to 22 on each side ; 

 3 shields between the occipital and the dorsal, 12 between the dorsal and the caudal. 

 Olive ; dorsal and caudal fins with black spots, which may form two curved bands on 

 the lower lobe of the caudal. 



Total length 65 millim. 



Numerous specimens from Descalvados, Matto Grosso. 



The fish described and figured by Steindachner as //. thoracatum, Gthr., belongs to a 

 distinct species, for which I have proposed the name H. steindachneri. His H. bilo- 

 batum is distinct from Cope's, which I regard as identical with II. thoracatum, and 

 is the same as that named by me H. guentheri. In fact, 3 species are confounded 

 under H. thoracatum in Dr. and Mrs. Eigenmann's Synopsis : they are distinguishable 

 as follows : — 



I. Throat entirely naked in front of the two pairs of pectoral shields ; 6 to 8 pairs of ventral 

 shields separated by a series of azygos shields; spine of adipose fin present; caudal deeply 



emarginate, middle rays half as long as outer H. thoracatum, Gthr. 



II. A transverse series of four shields in front of the pectoral shields ; 3 to 7 pairs of ventral shields 

 and a single azygos shield in front ; posterior dorsal spine usually absent. 

 Pectoral spine not reaching origin of anal ; caudal deeply emarginate, middle rays half as lono- 



as outer H. guentheri, Blgr. 



Pectoral spine reaching origin of anal ; caudal less deeply emarginate, middle rays much more 

 than half as long as outer H. steindachneri, Blgr. 



