126 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
SUMMARY OF THE FOREGOING COMPARISONS. 
• 
1. The Pacific Acii)enser traibsmoiitamis has a maximum of 7 more dorsal rays 
than any of the Atlantic species. 
2. Ill the CatostomidfCj we have the genus Xyrauchen with 1 to 2 more rays than 
any of the Atlantic genera of Catostomimc and the genus Catostomus with species 
having 2 more dorsal rays than any of the Atlantic species of the same genus. 
d. In the Gyprinida', Lepidomeda and Meda differ from all other American species 
m the development of spines in the dorsal tin. The genera Acrocheilm, Lavinia, 
Pogonichthys, Gila, and the subgenera Bichardsonms, S(pia,lius, and Cheonda all have 
more rays than their Atlantic relatives. The greatest absolute gain in the number of 
rays over all Atlantic slope species amounts sometimes to S rays. To offset this we 
have only some species of Notropis and N’otemigonus with rays exceeding the usual 
number on the Pacific slope. In this family both the modifications are found. 
4. In the SaltHonkln’, the species of the genus OncorJtynchus have 13 to 17 anal rays, 
while the highest number in the Atlantic species reaches no more than 11 rays. 
Thymallm, on the other hand, has a larger number of dorsal rays than any other 
American salmonoid. 
5. In tlie Percopsidw, the feeble armature of Fercopsis is changed into the strong 
spines of C(dnml>ia. 
0. In the Gasterofiteida’, Pygosteit.s hrachypoda and GasterontenH a-Uliamsoni have 
each 1 more dorsal siiine than any of their Atlantic congeners. 
7. In the Ceuirarchidcc we have an absolute gain of 1 dorsal spine over all 
Atlantic slope genera, while the gain is 2 dorsal spines and 1 anal spine in ArchopUtes 
as compared with its nearest relative AmJdoplites. 
8. Finally in the Cottidce, Coitus asper reaches a higher number of dorsal spines 
and rays and of anal rays than is ever reached in the numerous Atlantic slope species 
of this genus. The average number of dorsal spines is 1 more on the Pacific slope 
than on the Atlantic slope, while the average number of anal rays is higher by 2. 
These data fully warrant the statement made at the beginning ofthis chapter that 
“ 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 representatives modified in one 
or the other of two directions: There is either a larger number of rays or spines in 
the fins, or some of the rays have become modified into spines.” 
