324 MEMOIRS OF THE CARNEGIE MUSEUM. 



Table of Measurements. 



Length over all '. . 55 mm. 



Length to base of caudal ' 47 mm. 



Length of head to tip of opercular spines 8 mm. 



Distance of origin of dorsal from snout 30 mm. 



Distance of origin of dorsal from middle caudal rays 17 mm. 



Outer pectoral ray S mm. 



Maxillary barbel •. 11 mm. 



Nasal barbel 8 mm. 



Length of eye 1 mm. 



Length of snout 3.5 mm. 



Interocular distance 2 mm. 



This si^ecies is very similar to driatum, and may be a synonym of it. 



43. P*ygidium retropinne (Regan). 

 Trichomycterus retropinnis Regan, Ann. & Mag. Nat. Hist. (7), XII, Dec, 1903, 



p. 624 (headwaters of Magdalena east of Papaganat, St. Augustine, Andes of 



Colombia, 5,000 ft.). 



Habitat. — Headwaters of the Rio Magdalena. 



" Length of head 5| times in the total length. Head as broad as long. Diam- 

 eter of eye about 4 times in the interocular width, which is 3.33 times in the length 

 of the head. Snout as long as the postorbital part of head. Barbels equal to 

 about .8 the length of head. Dorsal with six branched rays, originating above or 

 slightly behind the anal opening, the distance from its point of origin to the caudal 

 2.4 times in the distance from the former to the tip of the snout. Anal with 4 

 branched rays, originating below the anterior third of the dorsal, the distance from 

 the base of its last ray to the caudal 5.4 times in the total length. Longest branched 

 ray of the pectoral, .66 the length of the simple outer ray, which is equal to it the 

 length of head. Ventrals not quite reaching the anal opening. Caudal truncate- 

 rounded. Brownish, with an indistinct darker stripe along the middle of the side 

 and traces of some dark spots." 



"Total length 80 mm." 



"A third specimen, 30 mm. in total length, which I have purposely excluded 

 from the above diagnosis, has a well-marked broad longitudinal stripe on each side. 

 In it the longest branched ray of the pectoral is ^ the length of the outer simple ray, 

 and the distance from the origin of the dorsal to the caudal is 2.2 times in the dis- 

 tance from the former to the tip of the snout." 



Key to the Species of Pycudium from the Amazon to the Esseqdibo. 

 From the vast lowland area of the Amazon, Orinoco, and Guiana but few species are known. 

 a. Origin of the dorsal in front of the vertical from the origin of the anal; ma.xillary barbel reaching tip 



