508 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 
The dorsal and ventral contours are long, even curves; the base of 
the first dorsal is scarcely oblique; the dorsal contour of the snout 
is but little (or scarcely) concave. Greatest depth of body, 2.2 
(1.8 to 2.3) in length of head to end of membrane at angle of 
opercle; the greatest width of the body or head is about equal to the 
depth below the origin of the lateral line, and about equal to the 
depth of the head at the vertical passing through the hind margin 
of the orbit. The form of the head and trunk.is shown in figure 27, 
in which the width of the body is abnormally contracted, owing 
to the imperfect preservation of the type-specimen. The length 
of the snout is unusually variable in this, species, so variable that 
Smith and Radcliffe separated out the short-snouted specimens 
as a distinct “form,” alpha (figure 29). That two distinct groups 
are not represented may readily be seen by an examination of the 
following table: 
Table of measurements of snout in C. commutabilis. 
Form Eta, | Typical. Delta. Alpha. 
Statlomesetse a Sea ee eos as ee ee 54451, 53481, 5590 | 5590 | 51721) 5590 | 55891| 5589 | 5589 | 5589 
Text fPune sce see cesates dese see ae aaa [soins DT | ieee eee 28) | aisle 200 eres Baers eee 
Preocular-lengihas js ecerescse cece eee 2533) 2585 | Qian 2hoon| 245 I 2n6 2565 2o2 ead 2. 67 
‘Preoralilengthize.seac cacenicncle eee DEG el 2erdd) Aetoa| bose: ol 29) ||P onO mel yao am oeeL | 3.0 3.1 
Width atibase2s mgs s..saenecnss cece | 3.15 | 3.25 | 3.1 | 3.1 2.75 | 2.95 | 2:95 | 2.8 |'3.0 2.9 
Width at anterolateral angles?,.-.....-- Te Te ON lead | 1.0 | 0.9 | 0.95] 0.85} .09} .09]| 1.0 
Orbivimlsnoutssstessece ences cee see 1.6 | 1.6 | 1.65 | Hale |i det 1.35 | 1.35 | 1.35 | 1.26 | 1.3 
3 Mesoned inte Taek of head. 
2 Measured at end of ethmoid portion of infraorbital ridge, into length anterior to that point. 
The ridges of the head are covered by a single series of strong 
scales, excepting the infraorbital ridge behind the middle of the eye, 
where the scales are in two series. The occipital ridges diverge a 
little toward both ends; the least distance between them is contained 
2.2 (1.8 to 2.2) times in the interorbital width. The rounded margin 
of the preopercle is scarcely denticulate; the lower ventral angle of 
the subopercle is produced backward into a slender flap. The orbit 
is large, as usual in this group of species, but widely variable in 
size, being contained 3.9 (3.33 to 3.95) times in entire length of head 
and 1.25 (1.15 to 1.3) times in postorbital length of head. The 
variation in the size of the orbit is not correlated with the size of the 
specimens; the extremes are joined together by intermediate sizes. 
Least interorbital width, 1.38 (1.33 to 1.6) in postorbital length of 
head; least suborbital width, 2.9 (2.2 to 2.8). The upper jaw 
extends backward from below the anterior nostril (or immediately 
behind that vertical) almost (or quite) to below the hind margin 
of the orbit; the length of the upper jaw is contained 3.75 (8.35 to 
4.0) times in the head; barbel, 3.6 (3.5 to 6.0) in postorbital. Six 
branchiostegals; gill-membranes with a free fold across the isthmus. 
