EXPLORATIONS IN WESTERN CANADA, ETC. 
121 
The families of the Mississippi basin not yet found in the Saskatcliewan basin 
are: 
1. Leiiisosteidw. 
2. Aiuiidae. 
3. Chipeidae. 
4. DorosoruidiB. 
Twenty two specimens 
Ammoccetes tridentatus. 
Catostonms catostoiims. 
Catostomu.s maoroclieiln.s. 
Pantostens jordaiii. 
Acrocheilus alutacens. 
Agosia imbila. 
Ag'osia falcata. 
Catostomns inaeroclieilns. 
Agosia falcata shnswap. 
M y 1 o c h e i 1 n s e an i- i mi s . 
Ptyclioelieilns oregoneiisi.s. 
.5. AmblyopsidiB-. 
d. CyprinodoutidiB. 
7. Ilmbrida?. 
8. AnguillidiB. 
were taken in the Columbia. 
Ptycliocheilus oregonensis. 
Leiiciscus atrarins. 
Lcuciscus hydroplilox. 
Leneisens balteatns laterali.s. 
Coi'egouiis 'ndlliamsoiii. 
Coregonus conlteri. 
Salnio niykiss. 
Leuciscns balteatns. 
Leuciscus balteatn.s lateralis 
C o re go m i .s TV i 1 1 i a 111 so n i . 
9. AtherinidiB. 
10. Apliredoderidai. 
11. SerranidiB. 
They are: 
Salvelinns iiaiiiayciisli. 
Oucorbynclms tscliawytscha. 
C oliim b i a t r a u s in o ii t a n a . 
Cottus asper. 
Cottiis rhotlieiis. 
Cottus pbiloiiips. 
Lota lota macnlo.sa. 
Salmo mykiss. 
Oncorhynchiis tscliawytscha. 
Cottus asper. 
My 1 ocli ei 1 11 s c anr i 11 II s . 
The ten species taken in tlie Fraser system are: 
But one variety, Afjofiia falcata shnstcap^ was found in the Fraser that tyas not 
also found in the Columbia. [Leneisens halteatns has been taken by others in the 
Columbia system.) 
Several species of Oneorhynehus and Acipenser are known from the Columliia and 
from tlie Fraser which are not included in these numbers. 
STRUCTURAL PECULIARITIES OF THE FRESH-WATER FISHES OF THE 
PACIFIC SLOPE. 
Almost every family of fishes having representatives in the fresh waters of both 
the Atlantic and the Pacific slopes has one or more of its Pacific slope representatives 
modified in one or the other of two directions: There is either a larger number of 
rays or spines in one or more of the fins, or some of the rays have become modified 
into S])ines. The largest number of either dorsal or anal rays is almost always found 
in some Pacific slope .species, and the range of variation is always greater in the Pacific 
slope species than in the Atlantic slope species of the same family, although the num- 
ber of species is usually less. lu most cases the differences are just perceptilile, and, 
were it not for the consensus of differences in all groups they would stand for nothing. 
The most marked differences are found in those fishes which are generically distinct 
from their Atlantic slope relatives. In several cases these modifications themselves, 
aside from all others, are of generic importance, as in the genera AreliopUtes^ Meda, 
Lepidomeda, Colnmhia, and the subgenus Biehardsonius. 
The modifications of the same set of organs being iiractically of the same nature, 
are unquestionably due to one definite cause. What that cause is I am at present 
unable to say. A comparatively short swift water-course, as most of the Pacific 
rivers have, suggests itself at once, but, as will be seen under the head of “Local 
The PeU-omyzontulfn and Cenirarchidfr -wero not .secured by me, but Mr. A. .1. Woohmm found 
these families in the headwaters of the Red River system. 
