SPHENOPHRYNE - American Museum of Natural History

6 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 253
to transforming my crude sketches into realistic
drawings.
METHODS
ANATOMY: On most specimens examined I
made a suite of measurements with dial calipers
read to the closest 0.1 mm or, if appropriate,
I used an ocular micrometer in a binocular
dissecting microscope read to the
nearest 0.05 mm. Sex of the specimen was
apparent if the specimen was a male calling
when captured. Otherwise, males were determined
by the presence of vocal sac openings
(absent in two species) or by examination
of gonads, females were determined by
examination of gonads. With the exception
of a few dried preparations, descriptions of
osteology derive from cleared and stained
specimens (identified as ‘‘C&S’’ in lists of
specimens examined). Color descriptions of
living frogs are from my field notes and photographs,
supplemented by notes and photographs
provided by other collectors.
The following abbreviations pertain to
measurements made (with some exceptions)
on each specimen:
EN. Distance between anterior edge of
eye opening and center of external naris.
EY. Distance between anterior and posterior
edges of eye opening. It is sometimes
necessary to push the eyeball up from within
the mouth in order to approximate the condition
in life.
FD. Width of disc of third finger measured
at a right angle to the axis of the digit
with the disc flattened against a glass plate.
FT. Length of foot between proximal edge
of inner metatarsal elevation and tip of fourth
toe (see HD).
HD. Length of hand between proximal
edge of inner metacarpal elevation and tip of
third finger. Both hand and foot measurements
may have reduced accuracy owing to
the sometimes indistinct nature of the metacarpal
and metatarsal elevations and to the
difficulty of properly spreading the hands
and feet of indifferently preserved specimens.
HW. Head width at widest point, generally
at the level of the tympanum or jaw angle.
IN. Distance between centers (not medial
edges) of external nares.
SVL. Length from snout to vent—from
tip of snout to cloacal opening, with body
flattened if necessary.
TD. Width of disc of fourth toe measured
at a right angle to the axis of the digit with
the disc flattened against a glass plate.
TL. Tibia length, between heel and outer
surface of flexed knee.
TY. Diameter of tympanum, including
tympanic ring, measured horizontally. In
most species the ear is scarcely apparent externally
and hence it is difficult to measure
with accuracy.
Relative lengths of fingers and toes were
determined by placing them parallel to the
third finger or fourth toe; actual lengths were
not measured.
USE OF PROPORTIONS
Species of frogs usually differ in one or
more body proportions, and these differences
may be employed usefully in discriminating
among species. Differences may be evident
in comparisons of regressions of the measurements
of body parts against body size
(SVL), although overlap in ranges may hinder
the use of regression data in species discrimination.
I routinely calculated and plotted
regression data for samples of all species.
Ratios comparing body part size to SVL, of
course, suffer from the same difficulty; that
is, overlap between species ranges of ratios
may be so great that the differences in proportions,
although statistically and possibly
biologically significant, may be largely useless
for specific identification of individuals.
An effective method of overcoming this
problem utilizes two different ratios simultaneously,
in each of which the two species
being compared show different but overlapping
ranges of variation. The statement takes
this form or a variant thereof: ‘‘Ratio A less
than X and ratio B greater than Y, vs. ratio
A greater than X and ratio B less than Y.’’
A graphic presentation allows one to place a
given specimen in the spectrum of points.
Identifications may be greatly facilitated in
this manner.
Ratios present another problem, however.
Most proportions—at least those commonly