CITHAEICHTHYS.— ACHIEUS. 3 



Mazatlan, Chiapas, and the Rio Sapayo, Ecuador. 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, bat 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 1^ to 1 J- in the length ; right pectoral present 1. mazatlanus. 



II. Depth o£ body 1| to 2 in the length. 



Right pectoral present 2. fonsecensis. 



No pectoral fins 3. fasciatus. 



1. Achirus mazatlanus, Steind., 1869. 



Achirus mazatlanus, Jord. & Everm. Bull. U.S. Nat. Mus. xlvii. 1898^ p. 2698. 

 Ilab. Pacific Coast of Mexico, entering rivers. 



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I have examined three specimens, 70 to 140 mm. in total length, from Presidio and 

 Mazatlan. 



2. 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. 



Eab. 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 



