1722 Bulletin ^7, United States National Museum. 



Trunk-fishes with the carapace 3 -angled, the ventral surface flat or con- 

 cave, never carinate ; ca.rapace closed behind the 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 Ostracion only in the form of the carapace. The 

 median dorsal ridge of the 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 Ostracion. Although this character is a striking one it is 

 not one of high structural importance. Hollard and Bleeker have dis- 

 carded 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 arrange- 

 ment of the species of the genus/ 7 and we think it not improper to accord 

 generic distinction to the 3-angled species, as distinct from the more spe- 

 cialized 4-angled forms. (Shortened from Lactoria, a milk-cow, 6<t>pv$, 

 eyebrow, from the projecting horns of Lactophrys Iricornis.) 



RHINESOMUS (P^TJ, file; o-w/oia, body): 



a. Carapace without spines anywhere. TRIQUETER, 2139. 



aa. Carapace with distinct spines, at least on the ventral ridges behind. 

 b. Frontal spines none. 

 CHAPINUS (Chapin, the Spanish name) : 



c. Carapace open behind the dorsal fin ; body everywhere with round dark 



Spots. BICAUDALIS, 2140. 



LACTOPHRYS : 



cc. Carapace closed behind the dorsal fin ; body mottled with paler. 



TRIGONUS, 2141. 

 ACANTHOSTRACION (a<av0a, spine; 6(TTpa/aoi>, a little box) : 



bb. Frontal region with 2 strong spines like horns. TRICORNIS, 2142. 



Subgenus RHINESOMUS, Swainson. 

 2139. LACTOPHRYS TRIQUETER (Linnaeus). 



(TRUNK-FISH; EOCK SHELLFISH; DRUNKEN-FISH; CHAPIN; PLATE-FISH.) 



Head 4; depth 2; eye 8 to 9 in total length, 4 to 4| in height of side. 

 D. 10; A. 10; P. 12; scales 9. Carapace trigonal, without spines; breadth 

 equal to % length of body in adults, greater in young. Ventral surface of 

 carapace convex anteriorly, concave posteriorly. Back elevated, com- 

 pressed, sides joining at an angle of about 30 degrees. Carapace con- 

 tinuous behind dorsal fin. Interorbital space concave. Upper surface of 

 snout concave. Teeth long, spike-like, 8 to 10 in each jaw. Scales of the 

 sides hexagonal, in young with stria3 radiating from center to angles of 

 each scale, in adult armed simply with tubercles, 9 to 10 in longitudinal 

 series from gill opening to tail, 8 in median line of ventral surface, 8 

 between ventral keel and angle of back ; posterior dorsal scute unarmed. 

 Branchial aperture oblique, its length greater than diameter of eye, 

 descending before base of pectoral. Fins obtusely rounded; caudal of 

 moderate length and rounded. Dark brown, thickly studded with cir- 

 cular spots of yellowish white, each about of an inch in diame- 



