XXV. THYRINOPS 61 



pressed belly, in the somewhat shorter and less pointed and less falcate 

 pectoral, and in the shorter anal fin ; in evermanni there are 22 to 25 

 soft anal rays ; in twelve specimens of balsanus, 18 to 23. T. balsana 

 is more closely related to crystallina, but has the head usually longer, 

 the depth less, the pectoral fin slightly shorter, and the eye smaller. 

 Greatest depth of body in mature females, somewhat less than one- 

 fifth the total length to caudal; head, 4.0 to 4.4 (4.3 to 4.5 in adults of 

 crystallina) ; pectoral as long as head, or slightly shorter or slightly 

 longer ; eye of adult, less than one-third length of head. There are 

 either three or four spines in the first dorsal. The rami of the lower 

 jaw are scarcely elevated posteriorly, and the gape of the mouth is little 

 restricted posteriorly. 



94. Thyrina crystallina Jordan and Culver, 1895.-^*- 



Thyrina crystallina Jordan and Culver, Proc. Cal. Acad. Sci. (2), 5, 420, 1895; 



Jordan and Evermann, Bull. U. S. Nat. Mus., 47, pt. 1, 804, 1896; Meek, Puhl. 



Field Mus. (Zool), 5, 184, 1904. 

 Type-locality. — Lower course of the Rio Presidio, near Mazatlan. 

 Thyrina guatemalensis Regan, Biol. Centr.-Amer., Pisces, 64, 1907 (in part). 

 Range. — Fresh waters of the Rio Presidio (Rio Mazatlan), Mexico. 



The characters regarded as diagnostic in the distinction of this 

 species from evermanni, though not wholly constant, are yet probably 

 of taxonomic significance. For example, the soft anal rays in the types of 

 CRYSTALLINA Vary from 19 to 23, in the types of evermanni from 22 to 25. 



95. Thyrina evermanni Jordan and Culver, 1895.-^'- 

 (Plate V, Fig. 18) 

 Thyrina evermanni Jordan and Culver, Proc. Cal. Acad. Sci. (2), 5, 419, pi. 33, 

 1895; Jordan and Evermann, Bull. U. S. Nat. Mus., 47, pt. 1, 804, 1896; 

 4, pi. 125, fig. 340, 1900; Meek, Publ. Field Mus. (Zool.), 5, 184, 1904. 

 Type-locality. — Estuary of the Rio Presidio at Mazatlan, Mexico. 

 Thyrina guatemalensis Regan, Biol. Centr.-Amer., Pisces, 64, 1907 (in part). 

 Range. — Estuary of the Rio Presidio, Pacific slope of Mexico. 



XXV. THYRINOPS Hubbs, 1918. 



Thyrinops Hubbs, Proc. Acad. Nat. Sci. Phila., 69, 306, 1918. 



Orthotype. — Atherinichthys pachylepis Giinther. 

 Range. — Shores of the Panamaic Province. 



This genus contains a single known species, intermediate in most 

 respects between Thyrina and Atherinella, as indicated in the key 

 to the genera. As in Thyrina, the air bladder, showing through the 

 translucent flesh and scales, extends broadly backward a short distance 

 into the urosome. 



