156 



PAPERS FROM TORTUGAS LABORATORY vol. xxxiv 



Acanthurus hepatus (Linnaeus) 



Teuthis hepatus Linnaeus, Syst. nat., 12th ed., 1766, p. 507 — Carolina. 



Hepatus pawnee Breder, Bull. Bingham Oceanog. Coll., vol. 1, art. 1, 1927, p. 73, fig. 32 — 

 Glover Reef, off British Honduras. 



Common, very frequently in mixed schools with Acanthurus bahianus, from 

 the shore out. 



It is almost entirely herbivorous. With its food, however, it swallows much 

 foreign material, only one-quarter to one-third being the algae usually found in 

 its stomach. The stomach is large, rounded, laterally compressed, thick-walled, 

 and muscular. 



This species is changeable in coloration; often pale, rather bluish, then show- 

 ing eight or ten narrow vertical dark bands on the side. Where the bottom is 

 pale but rough, light fish and dark brown ones may be seen together; but on the 

 reef, commonly brown ones only are present. The caudal fin in the brown phase 

 may be bluish, more white toward the lancelet, at the base of which this color 

 ceases abruptly; or it may be brown like the body. 



Brassy and blue streaks of equal width slope down from above gill opening to 

 eye, and from eye to nostril; five postocular yellow streaks and three anteocular 

 ones present in a specimen before me; often another yellow one below the eye. 



The teeth in each jaw are uniserial, flattened, elongate, spatulate, with their 

 distal borders denticulate. They are not rooted in the premaxillaries or dentary, 

 or even ankylosed with them. The tough membrane, however, in which they are 

 set on the dentigerous surfaces allows them relatively little movement. 



Dorsal normally with 9 spines; anal with 3. Soft rays in a sample of 30 collected 

 at Tortugas are D. 24V2 to 25 1 / 2 ; A. 20 1 / /> to 24 V?- 



Hepatus pawnee Breder (see reference above) is the young of A. hepatus. In 

 10 cotypes examined, the fin supports were D. IX^ 1 /. to 25 1 / 4; A. ll\,22 l / 1 to 

 24 Vz- In a sample of 10 from Nassau harbor, in size and appearance quite like 

 Breder's material, the comparable counts were D. IX,24 I / 4 to 25%; A. III,22 1 / 4 to 

 24 1 /?. Three specimens from Bermuda, in addition to the normal count for fin 

 spines, have respectively 26V2, 25^4, and 24*4 dorsal rays; and 23J4, 22^, and 

 23V2 anal rays. In the specimen last indicated, which is 40 mm. in length, the 

 posterior margin of caudal fin is bordered by white, which with its rounded 

 profile distinguishes it readily from A. bahianus. A specimen of the latter, 43 

 mm. in length, has a relatively straight profile, and a white marginal crescent on 

 caudal fin, which where broadest covers the distal quarter of the central rays and 

 the web between. 



Atlantic coast of tropical America northward to Florida and sometimes to 

 Cape Cod. W. H. L. 



Acanthurus bahianus Castelnau 



Common everywhere in shallow water, except in the great sand wastes and in 

 Thalassia. Found about coral stacks, into and under which it ventures, though 

 it is really a fish of the open. Its distribution is essentially that of the algae which 



