CITHARICHTHYS.—ACHIRUS. 3 
Mazatlan, Chiapas, and the Rio Sapayo, Kcuador. The very closely allied C. spilopterus, 
Giinth., 1862, from the Atlantic coast, differs in having the head somewhat shorter and 
the eyes a little smaller, whilst the scales are usually more numerous; it appears to be 
more strictly marine than its Pacific representative. 
2. ACHIRUS, Lacep., 1803. 
Achirus, Jord. & Everm. Bull. U.S. Nat. Mus. xlvii. 1898, p. 2693. 
Eyes on the right side, small, close together. Mouth small; jaws with small teeth on the left side, but not 
on the right; palate toothless. Scales small, adherent, strongly ctenoid ; lateral line straight. Dorsal 
commencing on the snout, posteriorly free from the caudal; right ventral median and continuous with 
the anal; pectorals small or absent; caudal rounded. 
The three species known to occur in the rivers of Mexico and Central America are 
closely allied, and differ little in the size of the scales (65 to 85 in a longitudinal series), 
the number of fin-rays (dorsal 50-60, anal 36-46), or the coloration (brownish, usually 
spotted or clouded with darker and with very narrow blackish transverse stripes). 
Their distinctive features are shown in the following key :— 
I. Depth of body 14 to 12 in the length; right pectoral present . . . . . 1. mazatlanus. 
II. Depth of body 1} to 2 in the length. | 
Right pectoral present . 2. . . 1 ee ee ee eee ee wR fonsecensis. 
No pectoral fins . 2 1. ww ee ee ee eee ee ee we 8. fasciatus. 
1. Achirus mazatlanus, Steind., 1869. 
Achirus mazatlanus, Jord. & Everm. Bull. U.S. Nat. Mus. xlvii. 1898, p. 2698. 
Hab. Pacific Coast of Mexico, entering rivers. 
I have examined three specimens, 70 to 140 mm. in total length, from Presidio and 
Mazatlan. 
9. Achirus fonsecensis, Giinth., 1862. 
Solea fonsecensis, Giinth. Cat. Fish. iv. p. 475 (1862). 
Achirus fonsecensis, Jord. & Everm. Bull. U.S. Nat. Mus. xlvii. 1898, p. 2699. 
Hab. Pacific Coast of Mexico and Central America, entering rivers. 
I have examined the type, a specimen of 110 mm., from the Gulf of Fonseca, and 
some small examples from the Rio Presidio. 
3. Achirus fasciatus, Lacep., 1803. 
Solea achirus, Giinth. Cat. Fish. iv. p. 476 (1862). 
Achirus fasciatus, Jord. & Everm. Bull. U.S. Nat. Mus. xlvii. 1898, p. 2700. 
Hab. Atlantic Coasts of the Southern United States and Mexico, entering rivers. 
I have examined six examples, measuring up to 120 mm. in total length, from 
various localities. 
B2 
