PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 211 
than length of snout; width of head at front of eye equal to distance 
from tip of snout to posterior border of orbit. Rostral ridges moderately 
separated, slowly convergent anteriorly, but remaining separate as far 
as they can be traced. 
Mouth nearly straight, its breadth 24 in its distance from tip of snout. 
Length of nostril 13 in breadth of mouth, its anterior valve narrow, 
extending but a slight distance towards the inner margin. Vent some- 
what nearer tip of snout than base of caudal. 
Dorsal fins similar, subequal, separated by an interspace which is 23 
times the length of the first. Distance from posterior root of base of 
ventrals to first dorsal about equal to length of snout. Sides of tail 
with a conspicuous fold. 
Skin everywhere rough, with a fine, nearly uniform, shagreen. No 
spines along the rostral cartilages; a row of very small superciliary 
spines; one or two blunt spines on the shoulder-girdle; a series of low, 
bluntish spines along the median line of the back, becoming larger and 
farther apart posteriorly. Females without fimbriated appendage above 
tip of snout. 
Color light olivaceous gray; translucent spaces on each side of snout 
becoming whitish in spirits, as in related species. Disk with a number 
of round, clear, slate-colored spots, as large as eye, these arranged sym- 
metrically; one on middle of snout; one at the base of each rostral car- 
tilage; a series of 6 or 7 forming an elliptical figure around each orbit; 
one at base of each pectoral behind and outside each shoulder. Vertical 
fins and caudal fold pale. Lower side of disk pale; a large oblong, 
blackish blotch on lower side of tip of snout, extending backward nearly 
half way to mouth. Blackish blotches below on edge of base of snout 
sometimes present. 
This species is abundant in the astillero or estuary at Mazatlan, where 
it is known to the fishermen as “Guitarro.” Several specimens were 
obtained by Professor Gilbert, the largest 24 feet in length, all of them 
being females. These are numbered 28205, 28206, 29547, and 29602 
on the Museum Register. This species was at first identified by us 
with R&. leucorhynchus, but the discovery by Professor Gilbert of the 
latter species at Panama shows that the Mazatlan form is distinct, 
although closely related. 
The color of &. glaucostigma is very peculiar and distinctive. The 
bluish spots do not disappear in spirits. 
INDIANA UNIVERSITY, April 25, 1883. 
