OCT., 1907. FRESH-WATER FISHES MEEK. 147 



eye 2.5 to 2.7; pectoral reaching nearly to middle of ventrals, its 

 length i.i to 1.2; origin of dorsal in advance of that'of anal, .its dis- 

 tance from tip to snout 1.6 to 1.8 in body; depth of caudal peduncle 

 i .3 to i .6 iri head ; dorsal of male much higher than that of female. 



Color light olivaceous ; dorsal in female light with a few black dots ; 

 other fins plain ; dorsal of male nearly uniformly blackish on lower 

 half, then slightly spotted becoming plain on distal fifth ; a large black 

 blotch on caudal peduncle extending on proximal half of the caudal 

 fin, other fins plain. 



Turrialba, 600 meters (2), 59 and 62 mm. 



Pcecilia tenuis sp. nov. OLOMINA. 



Type No. 6028, F. M. N. H. ; length 64 mm. ; Tiribi, Costa Rica. 



Head 3.8 to 3.9; depth 4.0 to 4.5; D. 8 or 9; A. 7 ; scales 31. 

 Body elongate slender, much compressed posteriorly; top of head 

 flat, interorbital 1.8 in head; diameter of eye 3.2 to 3.5; snout 3.9 to 

 4.1; origin of dorsal slightly in advance of anal (in female), its dis- 

 tance from tip of snout 1.7 in body; pectoral reaching middle of ven- 

 tral, its length i.i to 1.2 in head; depth of caudal peduncle 1.5 to 1.6 

 in head. 



Color olivaceous without stripes or bars, a black spot on base of 

 dorsal fin, above which are a few black dots, other fins plain. 



Tiribi, 1160 meters (2), 64 and 70 mm.; San Jose (2), 45 and 55 

 mm., Rio Maria Aguilar (2), 45 and 50 mm. * 



Family Mugilidse. 



Agonostomus monticola (Bancroft). 



Head 3.69; depth 3.67; D. iv- i, 8; A. ii, 9; scales 42; maxillary 

 reaching vertical from anterior margin of pupil, its length 3.76 in head ; 

 diameter of eye 3.47; distance between origins of two dorsals 1.06 in 

 head; longest dorsal spine 1.57 ; pectoral reaching slightly past origin 

 of anal fin; lips moderately thick. 



Individuals of this species under 80 mm. in length have very thin 

 lips, those longer than 100 mm. have thick lips. The lower jaw be- 

 comes shorter in the individuals with the thickest lips. From a con- 

 siderable series of this species examined by me it appears that the lips 

 thicken and the lower jaw shortens with age. The growth of fishes is 

 not uniform, and one must not expect the largest individuals are al- 



