64 PERCESOCES. 
1. Thyrina guatemalensis. 
Atherinichthys guatemalensis, Giinth. Proc. Zool. Soc. 1864, p. 1511, and Trans. Zool. Soe. vi. 
1869, p. 443°. 
Thyrina evermanni, Jord. & Culv. Proc. Calif. Ac. Sci. (2) v. 1895, p. 419°; Jord. & Everm. 
Bull. U.S. Nat. Mus. xlvii. 1896, p. 804*; Meek, Publ. Columbian Mus., Zool. v. 1904, 
p. 184°. 
Thyrina crystallina, Jord. & Culv. t. c. p. 420°; Jord. & Everm. 1. c.*; Meek, l. c.”. 
Menidia guatemalensis, Jord. & Everm. t. c. p. 801°. 
Melaniris balsanus, Meek, t. c. p. 183, fig. 64°°. 
Depth of body 4 to 5 in the length, length of head 43 to 43. Snout shorter than eye, the diameter of which 
is 22 to 3 in the length of head; interorbital width 24 in the length of head. Teeth in bands, the 
outermost series enlarged; jaws equal anteriorly ; maxillary not exposed, extending nearly to below 
the eye. 16 or 17 gill-rakers on the lower part of the anterior arch. Scales with entire edges, 36 to 42 
in a longitudinal series. Dorsal III-IV, I 7-9; origin of spinous dorsal above sixth ray of anal. 
Anal I 19-25, ending below or a little behind the end of the second dorsal. Pectoral falcate, longer 
than the head, extending beyond the middle of ventrals. Caudal forked, the lower lobe somewhat the 
longer. Caudal peduncle 13 to 2 as long as deep. 
Hab. Pacific Coast Rivers and Lakes of Mexico and Central America, perhaps 
entering the sea: 
Rio Presidio 3 § and Rio Balsas 1° in Mexico; Huamuchal ! ? in Guatemala. 
Here described from the types of the species from Huamuchal (Salvin), and 
co-types of JT. evermanni and T. erystallina from the Rio Presidio and of M. balsanus 
from the Rio Balsas, several specimens measuring up to 85 mm. in total length. 
Estuarine specimens have the pectoral fins longer and more acute than those from 
inland localities. 7. pachylepis, from the Coast of Panama, is closely allied, but has 
laciniate scales. Gill and Bransford (Proc. Ac. Philad. 1877, p. 187) record 
T. guatemalensis from Lake Nicaragua, but this identification must be regarded as 
probably incorrect. 
3. XENATHERINA, gen. nov. 
The very aberrant little Atherine described by Meek under the name of Menidia 
lisa may be regarded as the type of a genus distinct from Chirostoma, characterized 
by the mouth extending to below the eye and by the peculiar dispcsition of the 
scales. 
1. Xenatherina lisa. 
Menidia lisa, Meek, Publ. Columbian Mus., Zool. v. 1904, p. 182, fig. 63°. 
Depth of body 5 in the length, length of head 4. Snout shorter than eye, the diameter of which is 2} to 24 
in the length of head and greater than the interorbital width. Teeth small; mouth oblique ; jaws equal 
anteriorly ; maxillary extending to below anterior j of eye. 13 gill-rakers on the lower part of the 
anterior arch. Posterior part of body covered with scales, which are continued forward as a scaly band 
along the middle of the side; anterior part of body naked, except for a dorsal strip and a ventral patch 
