CHIROSTOMA.—THYRINA. 63 
Depth of body 4 in the length, length of head 37 to 34. Snout 1} to 1§ as long as eye, the diameter of which 
is 4 to 5 in the length of head; interorbital width 4% to 5 in the length of head. Teeth rather small ; 
lower jaw strongly projecting, a little more than 4 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 62 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 3 to ? the length of head, extending beyond the middle of the ventrals. Caudal forked. 
Caudal peduncle twice as long as deep. 
Hab. Mexico, Rio Lerma System : 
Lake Chapala!?4 (Buller, Jordan). 
Here described from several specimens, measuring up to 215 mm. in total length. 
14. Chirostoma sphyrena, (Tab. IX. fig. 2.) 
Chirostoma sphyrena, Bouleng. Ann. Mag. Nat. Hist. (7) v. 1900, p. 55°; Meek, Publ. Columbian 
Mus., Zool. v. 1904, p. 178, fig. 59°. 
Chirostoma lerme, Jord. & Snyd. t. c. p. 142, fig. 19°; Jord. & Everm. t. c. p. 3163‘; Meek, t. c. 
p- 179, fig. 61°. 
Depth of body 5% in the length, length of head 34. Snout 23 as long as eye, the diameter of which is 6 in 
the length of head; interorbital width 43 in the length of head. Teeth strong, in two series; lower jaw 
projecting, 4 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 11,5 spinous dorsal in advance of 
anal, its origin nearer to base of caudal than to tip of snout. Anal I 21. Pectoral nearly $ the length 
of head, extending to above the middle of ventrals. Caudal forked. Caudal peduncle twice as long 
as deep. 
Hab. Mexico, Rio Lerma System: 
Lake Chapala 1735 (Buller). 
Here described from the type, a specimen measuring 230 mm. in total length. 
Jordan and Snyder give the following numbers for C. lerm@:—Dorsal IV-V, 10-12. 
Anal 19-22. 54-68 scales in a longitudinal series. 
2. THYRINA, Jord. & Culv., 1895. 
Thyrina, Jord. & Everm. Bull. U.S. Nat. Mus. xlvii. 1896, p. 803. 
Melaniris, Meek, Publ. Columbian Mus., Zool. v. 1904, p. 183. 
Two species described by Giinther, 7. guatemalensis and T. pachylepis, are inter- 
mediate between Chirostoma and Atherinella, 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. 
