EIGENMANN I FRESH WATER FISHES. 247 



N. nigncajis and pallidns seem to be color varieties of N. iiiermis. 



Tail compressed, head depressed, the caudal peduncle about as deep 

 as the body. Head entirely covered with soft skin, little longer than wide, 

 its depth if-2 in its length. Eye small, superior; interocular width little 

 less than length of snout ; orbit without a free margin. Mouth wide, ter- 

 minal, each jaw with a rather deep band of villiform teeth. 



Gill-membranes narrowly joined to the isthmus. 



Anterior nasal opening with a barbel which is about \\ times as long 

 as the eye ; a series of pores extending from it backward below the eye ; 

 a prominent pair of pores between the eyes. 



Pectoral pore minute, above and behind the pectoral spine. 



Origin of dorsal fin one-fifth nearer tip of snout than to base of middle 

 caudal rays in specimens .12 meter long, one-fifth nearer base of caudal 

 rays than to tip of snout in a specimen .26 meter long. 



Margin of all the fins rounded. Caudal with numerous accessory rays, 

 the middle caudal rays \-\\ in the head. Origin of ventrals below or 

 slightly behind the first dorsal ray. Inner margin of pectoral spine ser- 

 rate, its lower surface spiny. 



Light brown mottled with darker, a series of about 5 light areas along 

 the lateral line ; fins speckled. 



Head 4^-3!; depth 7-6; D. 10; A. 11; Br. 10-12. 



This species does not belong to the tropical American fauna. Nor can 

 it technically be referred to the Patagonian fauna, since no specimens have 

 been recorded south of Central Chili. It occupies intermediate ground 

 and possibly touches the Patagonian region on its northwestern frontier. 



This account is based on material in the Museum of Comparative Zoology.' 



' PYGIDIUM Meyen. 



Trichomycteriis Valenciennes, Humboldt, Rec. d'Obs. Zool. et Anat. II, 348, 1833 {iiigricajis) not 



Thricliomyctenis H umboldt. 

 Thrychomyctems Cuv. & Val. XVIII, 485, 1846 (misquoted). 

 ThrichoDiycterits Girard, Proc. Acad. Nat. Sci. Phila., VII, 1854, 198; Girard, U. S. Nav 



Astron. Exped. II, 242, 1855 (misquoted). 

 Pygidiuin Meyen, Reise, I, 475, 1835 [fuscuni). 



Type: Pygidium fiiscuin Meyen. 



Habitat: Andes from Central Chili to Colombia; Callao Bay ; Amazon to Cudajas; South- 

 eastern Brazil ; Central Argentine Republic. 



The reasons for using the name Pygiduitn instead of the older Trichomycterus were given 

 by Eigenmann & Eigenmann, S. A. Nematognathi, 325. Inasmuch as some naturalists still per- 

 sist in using the name Trichoviycfmis, the statement made by us may be repeated : 



