412 CALIFORNIA ACADEMY OP SCIENCES. 



jenkinsi, the head is much larger and the form more ro- 

 bust, besides slight differences in the scales. The speci- 

 mens obtained were sent to us by Senor Ygnacio Moreno 

 after our departure from Mazatlan. 



Family PGECILIID^. 



53, Poecilia butleri Jordan. 



Common in the fresh waters of the Rio Presidio below 

 the village of Presidio, where the species was originally 

 taken by Mr. Alphonse Forrer. 



Head 3^ ; depth 2^ to 3^ ; dorsal 9; anal 6; scales 

 26-9; eye 3 in head, equal to snout; interorbital 2; pec- 

 toral 1/4^ in head; caudal equal to head. Longest dorsal 

 ray i/^ in head in male; 173 in female. 



Body much deeper and more compressed than in Poeci- 

 lia presidionis, the profile rather steeply rising to front of 

 dorsal. Dorsal and ventral outlines of head meeting at 

 mouth and forming a somewhat sharp point; snout as 

 viewed from above, truncate. Teeth in two series, the 

 inner smaller, more close set, not trifid, the two series 

 well separated. Interorbital space wide and flat, about 

 twice as wide as eye. 



The sexes differ greatly in the position of the anal fin, 

 it is under or rather behind dorsal in females, much in 

 front in males, the tips of ventrals reaching much past 

 the base of fin. The sexes similar in size, not very unlike 

 in coloration; both with traces of faint olive cross-bands, 

 especially on caudal peduncle; a dark curved streak be- 

 hind eye on opercle bounding a roundish silver}' area on 

 opercle and breast. 



Male green with pale blue spots on each scale sur- 

 rounded by pale bronze shades; no bars. Dorsal and 

 caudal pale orange, with many small black spots. Lower 

 fins pale. Female similar, paler, without cross-bands. 



