Cope.] 700 [May 17, 
ADDENDUM. 
PERCESOCES. 
MuaiILipz#. 
GASTROPTERUS ARCH&US, Gen. et. sp. nov. 
Char. Gen. A broad band of teeth on the premaxillary and dentary 
bones, and a patch on the vomer. Dorsal spinous fin with four rays. 
Ventral fins abdominal. Second dorsal opposite to anal. Dermal fold not 
crossing superior portion of premaxillary region, hence the jaws are only 
partially protractile. 
This genus is an interesting form, probably of Mugilida, related to Pro- 
tistius Cope, and Myzus Ginther. The wide bands of teeth, consisting 
of numerous series, are not found in the last named genus, but belong to 
the first. Here, however, the spinous dorsal fin is rudimental, and there are 
no teeth on the vomer. 
The pectoral fin has the elevated position usual in the Percesoces, but 
the ventral fin is more posterior than in Mugil, having the position usual 
in Physostomous fishes. The spinous dorsal fin is very small, and the cau- 
dal fin is forked. A lateral line of pores extends along the lower part of 
the side. 
The characters of this genus render it probable that Protistius* should 
be referred to the Percesoces. These forms add to the number of existing 
relationships between the cold blooded vertebrate faune of Australia and 
the West Coast of South America. 
Char. Specif. Radii. D. IV. L. 11; A. I. 15; V. 1.5; P. 15. The dorsal 
spines are very small, the first about as long as the diameter of the orbit, 
and originating above a point half way between the bases of the ventral 
and anal fins. The pectoral fin is wide, and extends three quarters way to 
the base of the ventral. The latter extends three-fifths the distance to the 
analfin. The anterior rays of the anal are much longer than the pos- 
terior, and the margin is concave. Caudal lobes sub-equal and acute. 
Scales, counting from spinous dorsal to ventral fin ; 20-93-3. Anterior to 
the ventral fin the scales become smaller and rather irregular along the 
lateral line. Between the occiput and first dorsal spine there are 50 rows. 
The top of the head is scaled to the line of the anterior borders of the 
orbits. 
The muzzle is prominent and parabolic in outline, projecting very little 
beyond the mandible. The outline of the latter is similar to that of the 
muzzle, and the mouth is horizontal to a point a half the eye’s diameter in 
front of the orbit, where itis cut off by the decurvature of the premaxil- 
lary bones. Orbit one-fifth the length of the head, and 15 times in length 
of muzzle, which is one mm. less than the slightly convex interobital 
space. The length of the head enters the total minus the caudal fin, four- 
times ; the greatest depth of the body enters the same, six times. Total 
# Procecd. Academy Phila., 1874, p. 66. 
