66 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 84 



MICRODESMUS RETBOPINNIS Jordan and Gilbert 



Figure 9, e; Figure 11, b; Plate 2, Figure 5 



Microdesmus retropinnis Jordan and Gilbert, Bull. U. S. Fish Comm., vol. 1, 

 p. 331, 1881 (1882) (Panama). — Jordan and Evermann, U. S. Nat. Mus. 

 Bull. 47, p. 2450, 1898. — Gilbert and Starks, Mem. California Acad. Sci., 

 vol. 4, p. 195, pi. 31, fig. 59, 1904 (Panama). — Meek and Hildebrand, 

 Publ. Field Mus. Nat. Hist., zool. ser., vol. 15, pt. 3, p. 955, 1928 (Panama). 



Body moderately elongate, somewhat compressed posteriorly, the 

 caudal portion, without fin, notably shorter than rest of body. Head 

 11.4 to 13 in standard length; depth 10.5 to 14.4; predorsal 3.2 to 3.7; 

 preanal 1.3 to 1.8; caudal 2.4 to 2.5; preventral 11.5 to 12; base of 

 ventrals to vent 2 to 2.7; snout 4.8 to 5 in head measured to upper end 

 of gill opening; interorbital 5.3 to 6.3. Dorsal 47 to 49, anal 30, pec- 

 toral 10, ventral 1-3. Eye small, high, lateral; mouth small, little 

 oblique, the gape not quite reaching anterior edge of orbit; lower jaw 

 strongly projecting with a small fleshy prominence at the symphysis; 

 lips with a free flange restricted laterally, the free edge of which does 

 not pass around the mouth anteriorly. Snout and lower jaw with pro- 

 nounced longitudinal swollen muscular ridges. Anterior nostril in a 

 minute pore at the oral end of the outer frontal ridge; posterior nostril 

 in a small round opening just before and above eye. Teeth com- 

 paratively strong, conical, in two irregular series in the jaws; no teeth 

 on the vomer or palatines. Gill openings restricted laterally, adnate 

 to the scapular region in front of the base of the upper fourth pectoral 

 ray, the aperture extending obliquely downward and forward to a 

 point in front of the lower pectoral ray, the openings not so long as the 

 width of the base of the fin. Body and head, except snout and lower 

 jaw, covered ^\dth minute nonimbricate scales imbedded in the skin; 

 at the base of the vertical fins on either side of the median line of the 

 back the arrangement of the rows of scales is notably differentiated 

 in that the rows diverge outward and backward following the direction 

 of the myomeric impressions. Scales with 39 radiating striae. Myo- 

 meres evident, 31 body and 26 caudal =57 muscular impressions. 

 Vertebrae, 32 body and 25 caudal=57. 



Origin of the dorsal fin more than two head-lengths behind the head, 

 or opposite a point midway between tip of lower jaw and the vent, or 

 a little nearer the former. Dorsal and anal fins long and low, similar, 

 but the anal much shorter, both fins joined to the caudal by mem- 

 brane. Ventrals very small, closely approximated and situated 

 slightly behind the base of the pectorals. Color brownish above 

 slightly paler below, upper part of sides with two longitudinal rows of 

 quadrate dark-brown spots; the upper series united over median line 

 of back and separated from the succeeding ones by light interspaces of 

 the ground color, forming faint cross bars on the predorsal region, 



