NATURAL SCIENCES OF PHILADELPHIA. 187 



Length of front operculum 9 



Height of operculum and suboperculum l(i 



Width of interorbital area 8k 



Eye Diameter 7\ 



Dorsal Origin from snout 32 



Length of base 31 + 13V 



Height at first spine 3i 



" " fifth spine s" 



" " lastspine 11 



" " longest ray 16 



" " last ray 9 



Anal Origin from snout 57 



Length of base 12 



Height at first spine 4 



" " second spine 7 



" " third spine 9~ 



" " longest ray 11 



" " last ray..." 8 



Caudal Length of median rays 19 



" ' longest rays 20 



Pectoral Length 16 



Ventral Length of spine 10 



" " first rav 23 



" fifth ray 10 



Hemichromis bimaculatus Gill. 



The form is similar to that of its congeners, and is highest under the fifth 

 and sixth dorsal spines, the height there somewhat exceeding a quarter ("26) 

 of the extreme length ; that of the caudal peduncle, behind the anal fin, 

 equals half of the greatest height, and that of the lowest part exceeds a ninth 

 (11 2) of the total length, and is considerably greater than the length of the 

 peduncle. The thickness of the body at the pectoral region equals half the 

 height (-13). 



The head forms three-tenths (*30) of the length ; its height at the preoper- 

 cular margin exceeds a fifth ( - 22), and that at the pupil nearly equals a sixth 

 (16) of the total length of the fish. The length of the snout equals an eleventh 

 (*9) of the same, and exceeds twice the height of the preoibital bone (*4). 

 The length of the operculum is twice as great as the height of preorbital (*8). 

 The eyes are oval, and the longitudinal diameter equals the length of the 

 operculum (-8), and is greater than the width of the forehead between them ; 

 the latter is plain, the emargination for the intermaxillary processes being 

 very shallow and extending little beyond the anterior borders of the orbits. 

 The mouth is small and oblique ; the supramaxillars extend backwards to the 

 anterior borders of the orbits. 



The larger teeth are moderate, uniserial and nearly or quite contiguous in 

 each jaw; there are about twenty on each side in the upper and seventeen in the 

 lower jaw, besides the two larger on each side in front in the upper and one 

 equal in size to the rest, but removed backwards on each side in the lower ; 

 the teeth of the inner, small, transverse row of the upper jaw are well devel- 

 oped, but much smaller than the outer, and two to four on each side separated 

 by a wide interval from those of the opposite side. 



The dorsal fin commences over the base of the pectoral, or at a distance 

 from the snout exceeding the head's length (*31) ; its spinous portion equals 

 28 of the total length, and its soft nearly an eighth (-12) ; the former in- 

 creases in a gradually curved line towards the soft portion, the first spine 

 being very short (*2i), the fourth more than twice as long (-6), and the last 

 nearly four times as long (*09). The soft portion is produced at the median 



1862.] 



