BULLETIN FLORIDA STATE MUSEUM


 Proportional measurements are expressed in thousandths of the
standard length (shortened hereafter to SL). These measurements
were tabulated initially in the form of frequency distributions by ma-
jor drainage areas for each member of the subgenus except N.
cerasinus. When inspection revealed no consistent geographical var-
iation in morphology except in N. albeolus, the proportional measure-
ments for all the others were combined in the final tabulations.
 Certain meristic counts for N. cornutus, N. albeolus, N. c. chryso-
cephalus, and N. c. isolepis were separated in the tables by major
drainage areas. This was done because the wide ranges of these
forms increases the possibilities for clinal or genetic variation. The
better to show the overall differences between N. cornutus living
east and west of the Appalachians, all populations in each of these
two areas were combined, with three exceptions: Those in the upper
Susquehanna and the St. Lawrence river systems are on or near the
drainage divide between the Atlantic Ocean and the Mississippi;
specimens from the streams in Maine and the Maritime provinces of
Canada show rather unusual meristic characters. Counts from all
areas were combined in the overall comparison of the Luxilus group.
 Vertebral counts were determined from X-ray photographs. The
procedures follow the methods discussed by Bailey and Gosline
(1955). The Weberian apparatus, regarded as containing four fused
vertebra, and the hypural plate were included in the counts. All
photographs were made with type M film and a "hard ray" machine
(Miller, 1957).
 The angle of the mouth to the top of the head was determined
with the aid of a special ocular as described by Smith (1956: 250).
With the pointer set at a 00 reading, the fish is placed on the stage
so that one crosshair (arbitrarily called the horizontal hair) in the
ocular lies directly over the length of the lateral opening of the mouth,
with the intersection of the crosshairs slightly anterior to the tip of
the snout. The ocular is then rotated clockwise until the vertical
crosshair touches the head at the posterior edge of the occiput. The
angle is then read in degrees to the nearest half degree.
 Inspection revealed that usually about 90 percent of the counts
 showed relatively little deviation from the mean of a normal distri-
 bution, while the extreme values dropped away rather sharply. As
 it is manifestly desirable to show this condition in a species account,
 the method shown in the following hypothetical examples was adopted
 to express it: A frequency distribution expressed as (22) 25 to 29 (38)
 indicates that 90 percent of the counts fall between 25 and 29, with


Vol. 8