1877.] 209 [Garman. 



Disk oval, truncate or concave in front. Snout without a promi- 

 nence. Head small, at the end of the anterior third of the disk. 

 Eyes very small, far apart, the only portions of the head appearing 

 above the level of the disk. Spiracle small, immediately behind the 

 eye, with a large rounded cartilaginous process on its hinder margin. 

 Nasal valves right angled, short, wide, confluent, attached in the mid- 

 dle, fringed on the posterior edge. Mouth small, regularly curved, with- 

 out papillae. Teeth small, subtriangular on the upper surface, ante- 

 rior side convex, inner edges and angle sharp, in eighteen series on 

 the upper jaw and seventeen on the lower. The bands of teeth do 

 not extend more than half way from the middle to the angle of the 

 mouth. Ventrals triangular, length equal the width when spread, 

 not reaching the margin of the pectorals. Tail less than one and a 

 half times the length of the disk, depressed in its entire length, with 

 a serrated spine near the extremities of the pectoral fins. The short 

 portion in front of the spine is stout, and is armed in the later stages 

 with irregular rows of sharp pointed, broad based tubercles; the pos- 

 terior portion is thread-like, and bears narrow membranous expan- 

 sions above and below. 



Young specimens without scales or tubercles, brownish yellow, with 

 lines or spots of brown, white below. At this stage the spiracles are 

 comparatively larger, and the portion of the disk in front of the eyes 

 shorter, truncate, or slightly convex. 



Medium sized yellowish brown, reticulated or spotted with brown, 

 covered on the upper surface with small harsh scales, with irregularly 

 placed long-pointed tubercles on the tail between the pectorals. 



Large examples are brown, uniform or with blotches of darker, 

 and have the margin in front of the head indented. On the lower 

 side the skin becomes very tough and leathery with age. The scales 

 bear a single cusp in the centre, and one on each of the three or 

 more narrowly compressed blade-like rays. 



Length of pectorals of medium sized specimen 12.3; from margin 

 to eyes 3.9; and width of disk 11.8 inches. 



Length of pectorals of young example 8.8; from margin to eyes 

 2.5; width of disk 7.7; tail from ventrals 13.1; and total length 21 

 inches. 



The Museum contains specimens from Para, Manaos and Obidos, 

 presented by the Thayer Expedition. 



