CHIEOSTOMA.— THYEINA. 63 



Depth of body 5 in the length, length of head 3j to 3^. Snout IJ to 1| as long as 63-6, the diameter of which 

 is 4 to 5 in the length of head ; iuterorbital width 4| to 5 in the length of head. Teeth rather small ; 

 lower jaw strongly projecting, a little more than i the length of head ; maxillary exposed distally, 

 extending to the vertical from the anterior margin of eye. 21 to 23 gill-rakers on the lower part of 

 anterior arch. Scales with crenate edges, 53 to G2 in a longitudinal series. Dorsal V-VI, I 11-13; 

 spinous dorsal in advance of anal, its origin nearer to base of caudal than to tip of snout. Anal I 20-22. 

 Pectoral | to ^ the length of head, extending beyond the middle of the veutrals. Caudal forked. 

 Caudal peduncle twice as long as deep. 



Ilab. Mexico, Eio Leima System : 



Lake Chapala^^* {Buller, Jordan). 



Here described from several specimens, measuring up to 215 mm. in total length. 



14. Chirostoma sphyrsena. (Tab. IX. %. 2.) 



Chirostoma sphyraina, Bouleng. Ann. Mag. Nat. Hist. (7) v. 1900, p. 55 ' ; Meek, Publ. Columbian 



Mus., Zool. V. 1904., p. 178, fig. 59'. 

 Chirostoma lermts, Jord. & Snyd. t. c. p. 142, fig. 19'; Jord. & Everm. t. c. p. 3163'; Meelv, t. c. 



p. 179, fig. 61 \ 



Depth of body 5| in the length, length of head 3i. Snout 2\ as long as eye, the diameter of which is 6 in 

 the length of head ; iuterorbital width 4| in the length of head. Teeth strong, in two series ; lower jaw 

 projecting, | the length of head ; maxillary extending nearly to the vertical from the anterior margin of 

 eye, its edge exposed for nearly its whole length. 22 gill-rakers on the lower part of the anterior arch. 

 Scales with crenate edges, 65 in a longitudinal series. Dorsal V, I 11 ; spinous dorsal in advance of 

 anal, its origin nearer to base of caudal than to tip of snout. Anal 1 21. Pectoral nearly | the length 

 of head, extending to above the middle of ventrals. Caudal forked. Caudal peduncle twice as long 

 as deep. 



Hah. Mexico, Rio Lerma System : 

 Lake Chapala i ^ 3 s (^Buller). 



Here described from the type, a specimen measuring 2.30 mm. in total length. 

 Jordan and Snyder give the following numbers for C. lermce: — Dorsal IV-V, 10-12. 

 Anal 19-22. 54-58 scales in a longitudinal series. 



2. THYRINA, Jord. & Culv., 1895. 



Thyrina, Jord. & Everm. Bull. U.S. Nat. Mus. slvii. 1896, p. 803. 

 Melaniris, Meek, Publ. Columbian Mus., Zool. v. 1904, p. 183. 



Two species described by Giinther, T. guatemalensis and T. pachjleins, are inter- 

 mediate between Chirostoma and Atherhiella, Steind., resembling the latter in the 

 posterior situation of the spinous dorsal fin and in the long falcate pectoral. The 

 abdominal region is more or less compressed, but not more so than in many species 

 of Chirostoma, and there is no trace of the ventral keel which characterizes 

 Atherinella. Melaniris was based on specimens preserved in formalin, with the 

 iris turned black. 



