350 FISHES OF WESTERN SOUTH AMERICA 
the diminished pressure at sea-level. Our Orestias come from a region having the 
atmospheric pressure two-fifths less than at sea level. This may account for the 
fact that they usually have the scaleless belly inverted to an unusual degree, in our 
collections, when transported to the greater pressures at low elevation. 
Although the published history of the genus Orestias is generally dated 1846, 
with the brief description, Valenciennes had first published a brief notice in the 
Institute, VII, p. 118, 1889. The type was not clearly stated but inferred in the 
Histoire Naturelle des Poissons, 1846, XVIII, at the bottom of page 225 and the top 
of page 226, where he says: ‘‘La premiére espéce de ce genre sera pour nous celle 
dont les individus paraissent atteindre 4 la plus grande taille, et qui ont dans leur 
dentition, dans le developpement de leurs boucliers granuleux et de leurs écailles, 
un ensemble de caractéres dont les autres espéces n’offriront que des modifications.” 
Thus O. cuvieri is well understood to be meant as his type. 
Prior to this time, however, Valenciennes informs us that at least two of the 
species were known, O. pentlandii and agassizii, at least to a small world, through 
drawings that had been made by M. Joseph de Jussieu, and transmitted to him by 
the grand-nephew, M. Adrien de Jussieu. 
Following this only a few small random collections were made by Castelnau 
in the 1850’s, Orton in the 60’s, and Agassiz and Garman in the 70’s. The second 
resulted in the publication of a few ill-considered species by Cope. The last- 
named were the basis of Garman’s very incomplete revision in the Cyprinodont 
report of 1895. An equally unsatisfactory report of the fishes resulted from the 
incidental collections made by MM. Créqui-Montfort and de la Grange in 1908, 
published by Pellegrin (1904, and 1906). Starks (1906) describes some 37 speci- 
mens from Titicaca, belonging to five species. In 1917 Evermann and Radcliffe 
brought together all the literature on the genus and assembled thirteen species 
which they could not remove from the list considered valid. 
While on the Irwin Expedition as traveling fellow of the University of Illinois 
my major efforts were given to the more elevated regions. It follows that Pygidium 
and Orestias were by far the greater part of my collections for some four months of 
my work in the highlands of central and southern Peru, Bolivia, and northern 
Chile. Some thousands of specimens of Orestias, large and small, were brought 
home. At intervals from that time until the death of Dr. Eigenmann I was working 
on them. In 1929, through error, the Orestias materials were sent to the California 
Academy of Sciences with the Jordan-Eigenmann collections. Other portions of 
the material had been sent to the University of Illinois. The following pages will 
show the results of the study of only a part of the entire material available. 
Many specimens were dissected for parasitological materials, and for stomach 
examinations. The field notes on food may be summarized as follows: 
Orestias agassizii. Intestine 1.5 times the length of the fish. Algal fila- 
ments, Cladocera, Amphipoda, insect fragments. No indication of shells or 
grit between scissor points. Specimens of small size from streams and shores 
with larger fragments of food, taken among water plants, than the larger species 
taken offshore, containing plankton. Those from shallows of Ascotan and Huan- 
cané had fed on Amphipods and insects. One specimen from R. de Eucaliptus 
