CHIEOSTOMA. 57 



Synopsis of the Genera found in the Fresh Waters of Mexico and Central America. 



I. Body completely scaled ; head scaly ; maxillary not extending beyond the vertical from the 



anterior margin of eye. 



Origin of sijinous dorsal in advance of the anal 1. Chirostoma. 



Origin of spinous dorsal posterior to that of the anal 2. Thyrina. 



II. Head and anterior part of body naked .3. Xenatherixa. 



1. CHIROSTOMA, Swains., 1839. 



Lethostole, Chirostoma, Kirtlandia, and Menidia, Jord. & Everm. Bull. U.S. Nat. Mus. xlvii. 

 1896, pp. 792, 794, & 796. 



About fifteen species from the coasts of Tropical and Subtropical America, some of 

 them entering rivers, and about as many fresh-water species from the Eio Lerma 

 System and the Valley of Mexico. 



Synopsis of the Mexican and Central-American Fresh-water Sjiecies. 



I. Length of head 3| to 4|- in the length of the fish. Jaws equal anteriorly or the lower 



projecting. Length of lower jaw less than ^ the length of head. 



A. Anal fin with I 12-15 rays; 45 to 57 scales in a longitudinal series ; 



17 or 18 gill-rakers on the lower part of the anterior arch ... 1. bartonl. 



B. Anal fin with I 14-17 rays. 



45 to 48 scales in a longitudinal scries ; 20 or 21 gill-rakers on the lower 



part of the anterior arch 2. patzcuaro. 



3G to 42 scales in a longitudinal series ; 11 or 13 gill-rakers on the lower 



part of the anterior arch 3. urge. 



C. Anal fin with I 16-21 rays. 



38 to 42 scales in a longitudinal series; 16 gill-rakers on the lower part of 



the anterior arch ; last dorsal spine above the origin of anal .... 4. jordani. 



38 to 45 scales in a longitudinal series; 15 or 16 gill-rakers on the lower 

 part of the anterior arch ; last dorsal spine in advance of the origin 

 of anal 5. breve. 



48 to 62 scales in a longitudinal series ; 16 to 19 gill-rakers on the lower 



part of the anterior arch 6. humboldtianiim . 



68 to 82 scales in a longitudinal series . 7. estor. 



44 to 51 scales in a longitudinal series ; 20 to 24 gill-rakers on the lower 



part of the anterior arch 8. chapalm. 



56 to 62 scales in a longitudinal series ; 21 to 23 gill-rakers on the lower 



part of the anterior arch 9. grandoculis. 



II. Length of head 3i in the length of the fish. Lower jaw shorter than 



the upper. Anal with I 19-20 rays. 53 to 56 scales in a longi- 

 tudinal series 10. jiromelas. 



BIOL. CEKTR.-AMEE., Pisces, May 1907. I 



