20 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I07 



A parallel comparison of B. tyrannus and B. patronus. — The prin- 

 cipal differences between tyrannus and patronus are shown in the 

 following parallel comparison. 



tyrannus 

 Body moderately deep, rather robust, 

 the ventral and dorsal outlines 

 more or less evenly convex ; usually 

 only half of greatest depth below a 

 straight line extending through lower 

 margin of eye to middle of base of 

 caudal ; greatest depth generally over 

 tip of pectoral fin, about two diame- 

 ters of eye behind margin of opercle, 

 30 to 40, usually 32 to 37 percent of 

 standard length, average in 232 spe- 

 cimens 34.2 percent. 



Head moderately small, somewhat 

 pointed, its length 28 to 36, usually 

 31 to 34 percent of standard length, 

 average in 211 specimens 32.2 per- 

 cent; its depth 25 to 32, usually 26 

 to 30 percent of standard length, 

 average in 203 specimens 27.8 per- 

 cent. 



Scaly sheath at base of dorsal com- 

 posed for the most part of a single 

 row of scales, not extending above 

 basal third of the shortest rays, and 

 not completely covering the fin if 

 deflexed. 



Scales moderately large, 41 to 55, 

 most frequently 45 to 52, average 

 48.2 in 135 specimens, if oblique 

 series crossing middle of side are 

 counted. 



Modified scales on back in front of 

 dorsal fin rather numerous, with 

 long hairlike pectinations in large 

 examples 31 to 43, most frequently 

 33 to 39, average ^^ in 195 speci- 

 mens. 



Caudal fin moderately short, the lower 

 lobe about as long as head, 25 to 35, 

 usually 26 to 33 percent of standard 

 length, average 29.4 percent in 214 

 specimens. 



patronus 



Body usually deeper, more strongly 

 compressed, the ventral outline much 

 more strongly convex than the 

 dorsal ; notably more than half the 

 greatest depth below a straight line 

 extending through lower margin of 

 eye to middle of base of caudal; 

 greatest depth at or near beginning 

 of posterior third of pectoral fin, 

 only about an eye's diameter behind 

 margin of opercle, 33 to 45, usually 

 35 to 42 percent of standard length, 

 average in 248 specimens 38.8 per- 

 cent. 



Head generally larger, blunter, its 

 length 31 to 38, usually 32 to 34.5 

 percent of standard length, average 

 in 274 specimens 33.6 percent; its 

 depth 29 to 37, usually 31 to 36 per- 

 cent of standard length, average in 

 158 specimens 33.5 percent. 



Scaly sheath at base of dorsal notably 

 higher, composed for the most part 

 of two rows of scales, covering basal 

 two-thirds of shortest rays, and 

 covering the fin, except for the 

 rays extending backward beyond the 

 sheath if deflexed. 



Scales somewhat larger, 36 to 50, 

 most frequently 38 to 46, average 

 41.7 in 116 specimens, if counted as 

 in tyrannus. 



Modified scales on back in front of 

 dorsal fin generally fewer, with 

 shorter pectinations in examples of 

 equal size, 24 to 33, most frequently 

 25 to 31, average 28 in 103 speci- 

 mens. 



Caudal fin rather longer, the lower 

 lobe often longer than head, 31 to 

 39, usually 32 to 36.5 percent of 

 standard length, average 34.5 percent 

 in 69 specimens. 



