38 



PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



Btevoortia pectinata, (Jenyns) Gill. 



Diagnosis. — Proportions of head and jaws as in B, tyrannus. Height 

 of body almost three-eighths of total length, and greater proportionally 

 than in B. tyrannus. Fins nearly as in B. tyrannus, but uniformly aver- 

 aging slightly more; the height of the dorsal somewhat less than three- 

 twentieths of total length ; that of the anal equal to or slightly less 

 than half the length of the maxillary. The caudal fin is somewhat 

 longer and more furcate, the length of the external rays never being less 

 than five-sixths of the length of the head, while that of the medial rays 

 remains proportionally the same as in the species first described. Inser- 

 tion of ventral somewhat behind tip of pectoral, this tin and the dorsal 

 being uuiformly somewhat farther back than in B. tyrannus ; the inser- 

 tion of the latter from one to four one-hundredths posterior to a point 

 equidistant from the snout and the base of the median caudal rays, and, 

 as in B. tyrannus, behind the vertical from the insertion of the ventrals. 



Scales very large, considerably serrated, and arranged regularly in 

 18 to 20 transverse and 50 longitudinal rows. Scales forming sheath at 

 base of pectoral not large. Operculum smooth, or with inconspicuous 

 and few striations. Squamation upou lobes of caudal extensive and 

 conspicuous. 



Variations. — The variations in the individual specimens studied are 

 not of great importance, and are indicated in the table of measure- 

 ments. 



Table of Measurements. 



Current number of specimen. 

 Locality 



Extreme length 



Body : 



Greatest height 



Head: 



Greatest length 



Distance from snout to nape 



Length of maxillary 



Length of mandible 



Dorsal : 



Distance from snout 



Length of longest ray 



Length of last ray 



Anal : 



Distance from snout 



Length cf longest ray 



Length of last ray 



Caudal : 



Length of middle rays 



Length of external rays, superior 

 inferior . 

 Pectoral : 



Distance from snout 



Distance of tip from snout 



Length 



Ventral; 



Distance from snont 



Length 



Dorsal rays 



Anal rays 



Number of scales in lateral line 



Nunibei' ol l):,n>i verse rows 



1709. 

 Paraguay. 



Millim. lOOths, 



II. 17 

 I. 21 

 abt. 50 

 abt. 20 



36 



33 

 21 



14i 



18" 



54 



m 



6" 



70J 

 7 

 6 



6i 



24 + 

 26 



32 

 .iO 



18 



9i 



M. C. Z. a. 

 Rio Grande. 



Millim. lOOths 



IL 17 

 I. 20 



4a 



20 



30 



21 

 13 

 16 



53 

 12 



6 



70 

 6 

 4 



6 

 25 



27 



29 

 47 

 17 



48 



8 



M. C. Z. b. 

 Eio Grande. 



Aver- 

 age. 



Millim. 



IL 17 

 I. 20 



49 

 20 



lOOths. lOOths. 



31 

 •21 

 14 

 17 



1-2 



30^ 



48 



nf 



49.i 



8J 



