49 o Memoir Sears Foundation for Marine Research 



Spiracles: length 1.4, 1.7; distance between 17.5, 18.9. 



Mouth: breadth 12.8, 13.6. 



Exposed nostrils: distance between inner ends 10.5, 11.9. 



Gill openings: (average of both sides) length, ist 5.7, 6.0; 3rd 5.9, 6.7; 5th 4.1, 



4.4; distance between inner ends, ist 13.7, 15.1; 5th 3.7, 4.5. 

 Dorsal fin: vertical height 4.0, 4.6; length of base 5.1, 6.3. 

 Pelvics: anterior (outer) margin 6.7, 6.^. 

 Distance: from center of snout to center of cloaca 40.2, 44.3; from center of 



cloaca to tip of tail 68.2, 71.0. 



Disc, exclusive of cephalic fins, about twice as broad as long, with well marked 

 mid-dorsal crest from nuchal region to pectoral girdle; its thickness at pectoral girdle 

 (where thickest) about 14 "/o as great as breadth of disc from tip to tip. Tail (if intact) 

 from center of cloaca at least 1.5 times as long as body from center of cloaca to front of 

 head;*' moderately stout below dorsal fin, tapering gradually rearward to lash-like tip 

 and strongly compressed laterally throughout its length; its anterior part, opposite 

 posterior end of dorsal, about 1.5 times as high as wide; its sides rounded below dorsal 

 fin but nearly flat rearward from latter; upper surface of tail with a faintly indicated 

 median ridge for a short distance posterior to dorsal fin; skin not reticulate.'" 



No tail spine. 



Skin of small specimens naked except for a few soft minute spines on trifid bases 

 scattered along mid-dorsal belt of posterior part of disc; larger specimens with fine 

 prickles, either sparse or close-set, along median belt from head to dorsal fin ; also here 

 and there on pectorals; discs of some mature specimens perhaps more generally prickly; 

 upper surface of tail naked posterior to dorsal fin; lower surface of tail smooth, but 

 abdominal region more of less roughened with minute prickles. 



Head nearly flat above or weakly convex transversely, without longitudinal depres- 

 sion; its thickness at level of mouth a little more than 1/3 as great as breadth between 

 eyes; its dorsal profile sloping a little forward to sharp front margin; its anterior contour 

 weakly and evenly concave. Eyes on sides of head at about midlevel, nearly circular, 

 their diameter a little more than half as great as distance from mouth to front of head, 

 or about 13 % as great as width of head between orbits. Spiracle circular, with firm 

 rim, a little less than half as large as eye; about level with eye and posterior to posterior 

 margin of latter by a distance a little greater than diameter of eye; spiracular opening 

 preceded by a groove extending to above eye. 



Gill openings straight or slightly wavy in outline, their lengths on each side not 

 always equal ; first to fourth gill openings a little more than half as long as distance 

 between inner ends of exposed nostrils; fifth about 70—75 % as long as first; distance 

 between inner ends of first gills about 1.2 times as great as distance between inner 



89. Museum specimens are likely to have lost part of their tails. 



90. The skin close behind the dorsal fin is described as reticulate in Mobuhz lucasana of the Pacific Coast of Central 

 America (Beebe and Tee-Van, Zoologica N. Y., 23, 1938: 300). 



