BULLETIN OF THE UNITED STATES FISH COMMISSION. 
202 
Genus 122. LACTOPHRYS Swainson. Three-angled Trunk-fishes. 
Trunk-fishes with carapace 3-angled, ventral surface flat or concave, never carinate; carapace 
closed behind anal fin; carapace with or without frontal and abdominal spines; dorsal rays 9 or 10; 
caudal rays always 10. This genus contains 5 species, 4 of them American, and differs from the Old 
World genus Oslracion only in form of carapace. The median dorsal ridge of carapace is much more 
developed than the others, so that the body is 3-sided and 3-angled, instead of 4-sided and 4-angled, as 
in Ostrcirion. Although this character is a striking one, it is not one of high structural importance, 
llollard and Bleeker have discarded it as being of no real systematic value. All writers agree that the 
species of the group are most closely related, and that the relations of the species are closer than they 
appear. We think, with Dr. Goode, that the shape of the carapace affords “the most reliable guide 
in the arrangement of the species of the genus,” and we think it not improper to accord generic 
distinction to the 3-angled species, as distinct from the more specialized 4-angled forms. 
R HINF.SOMUS: 
a. Carapace without spines, anywhere triquetcr, 219 
an. Carapace with distinct spines, at least on the ventral ridges behind. 
b. Frontal spines none. 
Chapinus: 
c. Carapace closed behind dorsal tint body everywhere with round, dark spots bicaudalis, 220 
Lactophrys: 
cc. Carapace open behind dorsal fin; body mottled with paler trigonus, 221 
Acanthostracion: 
bb. Frontal region with 2 strong spines like horns tricornis, 222 
219. Lactophrys triqueter (Linnaeus). “Chapin” ; Trunk- fish. 
Head 3.5; height of side about 2; greatest ventral width 2.6; eye 3.4; snout 1.4; interorbital 1.7; 
least depth of caudal peduncle 4.1, its width in its depth 2.5; D. 10, its base 3.7 in head, the height 
1.6; A. 10, its base equal to that of dorsal, its height a little less; P. 11 or 12, 1.6 in head. Body 
sharply 3-angled, sides rather double concave; dorsal carina strongly arched, more so than in L. bicau- 
dalis, ending anteriorly above eye; ventral angles more convex and flaring than in L. bicaudalis-, 
supraoccipital ridge less strong, continued backward along side in a low, flat, ridge; profile from snout to 
eye somewhat concave; interorbital space concave; ventral surface slightly convex anteriorly, posteri- 
orly with two low ridges, the surface between them and between each and the ventral angle shallowly 
concave; scales of sides hexagonal, in young with strife radiating from center to angles of each scale, 
in adults armed simply with tubercles, 9 or 10 plates in horizontal series from gill-opening to tail, 8 in 
median line of ventral surface, 8 between ventral keel and back; posterior dorsal scute unarmed; cara- 
pace closed behind dorsal and anal, width behind dorsal about 1.75 that behind anal; carapace without 
spines anywhere; branchial aperture oblique, its length about 2.5 in head, greater than eye; dorsal, 
anal, and caudal obtusely rounded; pectoral triangular, first rays longest. 
Color in life: Body dirty white, upper third with small round white spots and some narrow black 
bars promiscuously arranged; head whiter and with whiter stellate spots; ventral angles with some 
