VOL. I. ] The Evolution of the Catfishes. 7 
by Sagemehl. Cope and Gill in their systems have derived the 
Nematognathi and Eventognathi from distinct sources. 
The Nematognathi are distinguished from the remaining Ostario- 
physiz by the absence of a suboperculum and the codssified supra- 
occipital and parietals, and, with one exception, by the vestigiary 
maxillary. In general appearance some members of the order ap- 
proach the Eventognathi so closely that even Valenciennes was mis- 
led by the superficial resemblance. In this paper only American 
forms are considered, but the series of Nematognathi from the low- 
est (Diplomystes) to the highest (Farlowella) living species is so com- 
plete among American species that I am led to believe that all exotic 
forms are descendants of emigrants from the Americas. Not many 
fossils of this order have been found, and those which have been 
discovered do not help us materially in determining the inter-rela- 
tions of the higher groups. 
The date of the differentiation of the orders of Ostariophysiz is 
uncertain. Silurine,* Bagariinze and Pimelodinzt} were separated 
as early as the beginning of the Tertiary, and as both these sub- 
families are quite remote from the most primitive living nematog- 
nathoid the Nematognathi must extend into the secondary period. 
The Nematognathi reach their highest development in the neo- 
tropics, where they constitute forty per cent. of the entire fresh-water 
_fish fauna. All the families,t subfamilies and genera now inhabiting 
this region have undoubtedly originated here. In most of the 
families the maxillary bone is a mere vestige and serves only as a 
support fora highly specialized dermal appendage, the maxillary 
barbel. So greatly has this bone been modified even in its develop- 
ment that Ryder§ seriously questioned whether the basal bone of 
the maxillary barbel in the North American cat fishes is in reality 
the vestige of a maxillary. No doubt need, however, be entertained 
on that score, since in Diplomystes the basal bone of the short 
primitive maxillary barbel is a functional dentiferous maxillary. 
The comparative development of the maxillary is, then, an excel- 
* Pseudeutropius and Bagarius, living Indian genera, have been found in tertiary 
deposits of the highlands of Padang in Sumatra. 
tLeidy, Contr. Ext. Vert. Fauna Western Ter., 192. The species recorded by 
him is in all probability a member of Cope’s Rhineastes. Cope, Ter. Verteb. 
_¢ The families of this order were defined by us in the Am. Nat., July, goa 
= the Development of Osseous Fishes, iiernees. ea 1886. 
