GILBERT AND STARKS — FISHES OF PANAMA BAY 19 



erroneous, as will appear by comparino; them with the above. The size of the spots 

 is somewhat variable, and the length of the tail is unreliable, the latter being usually 

 more or less shortened by injury. 



27. Myliobatis asperrimus (Gilbert). 



Plate III, Fig. 6. 

 Myliobatis asperrimus Gilbert, (Jordan & Evermann, 1898, p. 2754). 



Upper surface of head and body, excepting the snout, an area on outer side of spiracle, the 

 pectoral margin and its posterior angle, and the ventral fins, thickly covered with minute usually 

 stellate prickles of uniform size, most numerous on median portions of head and back; those qn basal 

 half or two-thirds of pectorals are least crowded, and are arranged in definite longitudinal series, 

 corresponding with the muscle bands. The tail is very rough throughout, being covered with similar 

 stellate prickles. It is also crossed by numerous narrow grooves, or indented lines, mostly convex 

 forwards, somewhat irregular in position and direction, and not corresponding on the two sides. In 

 the type they follow at an a\-erage inter\-al of about 10 mm. Lower side of disk mostly smooth, with 

 some prickles on the basal part of pectorals anteriorly, arranged in lengthwise series, and other patches 

 on lower side of head, belly and base of ventrals. 



Rostro-frontal fontanel scarcely constricted anteriorly, the bounding ridges diverging abruptly 

 at their anterior ends. Nasal flap with a shallow median notch, covering the mouth except the 

 median portion of lower dental plate, its posterior margin coarsely fringed. Teeth in each jaw in one 

 broad, median row, and three lateral rows; those of median row about five times as broad as long 

 antero-posteriorly. 



The color is dusky-brown above, the anterior portion of pectorals with eight or ten narrow, 

 transverse bars of bluish-white, most of which break up into series of spots towards outer margin of 

 disk, the posterior ones also breaking up towards middle line. The bars and spots are fainter 

 anteriorly, becoming whiter and more intense posteriorly. Towards outer angles of disk the bars are 

 sometimes separated by intermediate series of light round spots. The bars usually fail to meet across 

 the back. The posterior portion of disk, including base of tail and upper surface of ventrals, is 

 covered with round white spots not much larger than pupil; some of those immediately succeeding the 

 bars show a transverse serial arrangement. The top of head shows one or more pairs of indistinct 

 light spots. Margin of snout and of pectorals blackish. Spiracular border black. Dorsal with a black 

 blotch posteriorly. Under side of head and disk bright white. Proximal portion of tail blackish above, 

 lighter below, the entire tail becoming black posteriorly. 



mm. 



Length of disk to front of anus 272 



Length of disk to posterior edge of pectorals 338 



Width of disk 345 



Length of tail (not perfect) 1215 



Greatest width of head, at origin of pectorals 79 



Width of cranium, between orbits 45 



Width of snout, opposite front of eye 55 



Tip of snout to middle of nasal flap 60 



Length of nasal flap 26 



Greatest width of nasal flap 35 



Diameter of iris 10^ 



Width of mouth 33 



Distance between anterior gill-openings 75 



Distance between posterior gill-openings 45 



Distance from anterior to posterior gill-openings 45 



Length of spiracle 26 



Length of fontanel 60 



Greatest width (at anterior end) 23 



