Early measurements were made to the nearest millimeter; at later stages, 

 some measurements were made to the nearest centimetero The 19^9 measure- 

 ments and all subsequent work, were made to the nearest five millimeters. 

 In this paper, mean total lengths are reported to the nearest tenth of a 

 millimeter.. 



Some early measurements were made on the basis of standard length 

 and some on total length. The I9U9 measurements and some 19$0 measure- 

 ments were on the basis of fork length, but all measurements have been 

 brought into agreement through conversion to total length. Table 1 is a 

 conversion table treating standard, fork, and total lengths and is based 

 on measurements made on several thousand Yellowstone black-spotted trout 

 from Yellowstone Lake and its tributaries. These results will be discussed 

 below. 



Comparisons reported here have been made with the "t" test for com- 

 parison of means. Standard deviations of mean lengths and "t" values 

 are reported where they apply. 



Field measurements have been carefully screened before being used, 

 in order that reliable comparisons could be made. For instance, measure- 

 ments made over a period of only a few weeks have been discarded as not 

 representing an entire season's values. The spawning season usually lasts 

 eight to ten weeks, and the fishing season extends from May 30 to 

 October l5. Measurements from different parts of the lake and individual 

 stre ams have been treated separately. Comparisons between small numbers 

 of measurements have been avoided because they have usually not been rep- 

 resentative of their populations. 



CONVERSION FACTORS 



Table 1 relates measurements in standard, fork, and total lengths. 

 These data are based on thousands of measurements in which sexes, locali- 

 ties, and size ranges are combined. Relationships between standard length 

 and total length were found to vary between sexes and from place to place. 

 Hile (I9hl) discussed similar variations with respect to rock bass, and 

 showed that in the larger size groups males have longer tails than females. 

 This feature is seen in the present data relating to cutthroat trout. It 

 is reasonable to expect differences because of variation in method from per- 

 son to person or for extremes in size ranges to reflect growth character. 

 Carlander and Smith (19U5) mentioned a proportional shortening of the caudal 

 fin as perch, walleye pike, and crappies increase in lengths Beckman (I9U8) 

 reported that this was also true for bluegill, yellow perch, pumpkinseed, 

 smallmouth bass, largemouth bass, rock bass and northern pike in Michigan, 

 and Van Oosten noted it for sheepshead (1938) and Lake Huron whitefish (1939) . 



