CRITICAL NOTES ON MYLOCHEILUS LATERALIS AND LEUCISCUS 
CAURINUS. 
By JoHN OTTERBEIN SNYDER, 
Assistant Professor of Zoology, Leland Stanford Junior University. 
Girard 4, in 1856, placed Lewciscus caurinus Richardson? in the genus 
Mylocheilus along with M. lateralis Agassiz & Pickering’ and J. 
Jraterculus, which he described from Monterey, Cal. Mylocheclus has 
M. fraterculus has long been identified, no doubt correctly, with the 
form found in the Columbia River. 
Recent authors have not only continued to associate JZ. lateralis 
with Z. caurinus, but they have also considered the species identical, 
a proceeding wholly at variance with the facts. Richardson described 
a form closely resembling Ptychocheilus oregonensis, with which he 
says it was confused by the collector. He also observes? that P. 
oregonensis is so similar in general appearance to this species that it 
may readily be confounded with it. However, a comparison of the 
original descriptions of JZ. lateralis and LZ. caurinus will leave no 
doubt as to the distinctness of these two forms. Aside from the phar- 
yngeal teeth, which Richardson does not mention, his species differs 
from J. lateralis in the absence of a maxillary barbel’, in having 10 
dorsal and 9 anal rays, a longer snout and larger mouth, scales sub- 
orbicular in shape, and other less conspicuous characteristics. The 
Mylocheilus caurinus of recent authors is synonymous with WV. lateralis 
Agassiz & Pickering. 
While conducting explorations in Oregon under the direction of the 
United States Bureau of Fisheries the writer secured a specimen from 
the Willamette River, near Corvallis, which agrees almost perfectly 
aGirard, Charles, Proc. Ac. Nat. Sci. Phila., 1856, 169. Girard probably had specimens of M. 
lateralis which, on account of some slight individual variations, he identified as L. caurinus. He 
certainly did not have examples of the latter species as it is without barbels, 
b Richardson, John, Fauna Boreali-Americana, III, 304, 1836. 
¢ Agassiz, L., Am. Jour. Sci. Arts, XIX, 1855, 231. 
@ Richardson, op. cit., p. 305. 
e Richardson, op. cit., p. 120. ‘*The Leucisc?, or Daces, have a short dorsal and anal, are destitute 
of spinous rays or barbels, and exhibit nothing peculiar in the structure of their lips.” 
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