They are merely short or unassociated. arCs; or If- they 



completely circle the sculptured part, they are usually not 

 concentric v,rith the margin; furthermore, they frequently 

 join an annulus at the base. In any case, they may be less 

 distinct than an annulus, being vague and indefinite, or 

 they may be much more distinct, having a scarlike appearance; 

 that is, with very pronounced irregularities of pattern, 

 the folds being broken or otherwise obviously abnormal (See 

 figures 21;, 27). They rarely appear in all the scales of 

 an individual 



For the first annulus, which is sometimes difficult to distinguish 

 from a scar, especially if it be nearer the center than normal, the 

 following rule v/as applied: A mark conforming to the above description 

 of an annulus V\ras counted as an annulus, provided it appeared in all 

 the scale specimens examined; but if in one or more specimens said mark 

 had an obviously scarlike appearance, it was considered a false annulus, 

 and was not counted. 



Although a false annulus may appear at any time during the year, 

 a true annulus is formed only once annually, and during a certain sea- 

 son. The distance between annulus and the margin of the scale — the 

 marginal increment — represents the grov/th since the annulus was formed. 

 For fish in their first year, the marginal increment is the distance 

 betv/een the base of the sculptured part and the margin of the scale. 

 If one were choosing unperiodic marks to determine age in samples of 

 fish, then frequency curves of the marginal increments should show no 

 progress in width during the year, for there should be no consistency 

 in the time of appearance or position of the marks. But, on the other 

 hand, if one were choosing truly annual marks, there should be one time 

 of year when the marginal increments are narro^;^est, and another time 

 when they are i\i.dest, with intermediate widths betvreen. This argument 

 is the basis for the follovj-ing test as to v;hether or not the annulus 

 is formed once yearly. 



A stratified random sample of 3,000 mounted scales was dravm (by 

 Mosher) so as to represent about equally all the months of the period 

 studied, and, where possible, to represent equally northern and southern 

 California material. The labels of the slides v/ere then masked, the 

 slides mixed, and dra\m at random from a box. The scales were then 

 examined (by walford), and measurements recorded as described above- 

 Since the annulus is not apparent at the time it is fonning on the very 

 edge of the scale, but only sometime afterward v^rhen enough marginal 

 growth has occurred to set it off clearly, no zero marginal increments 

 were recorded. Figure h shov/s the marginal increments thus measured 

 for scales with 0, 1, and 2 rings. 



Obviously in the specimens of these year classes examined, the 

 marginal increments vrere relatively narrow in April, 1938, and increased 

 in width from then until the folloviring fall, when narrow marginal in- 

 crements began to appear again. In other words, the marks called an- 

 nuli in this study must be really annual in occurrence, and may be used 

 to determine age, at least for the first two years of life. 



40 



