64 Memoir Sears Foundation for Marine Research 



of various sizes, but irregularly fluted or arrowhead-shaped anteriorly; those on either 

 side of rostral ridge spear-shaped and sharp-pointed with concave margins; those along 

 sides of tail generally ovate and more or less pointed; those along outer margins of 

 pectorals and of snout, around orbits, and along margins of spiracles, smaller, more 

 rounded, and more closely crowded. Usually 33—37 larger tubercles along midline of 

 back, from nuchal region to first dorsal; similar to smaller scales in shape, or more 

 pointed posteriorly, but varying widely in prominence (apparently irrespective of age or 

 sex); thorn-like on some but so slightly conspicuous on others as to be detected only 

 by touch or by examination with a lens; eight or nine smaller tubercles in interspace 

 between dorsal fins on some specimens ; some with one or two small tubercles on scapular 

 region on one side or on both; anterior and posterior sectors of orbital ridge with 

 enlarged flattish denticles in some cases. Tip of snout of typical specimens conspic- 

 uously armed with blunt conical tubercles or thorns, varying in number from 2-7 

 or perhaps even more in later stages of growth; see discussion (p. 53). Lower surface 

 as a whole clothed with minute, smooth, flattish, or slightly rounded denticles irreg- 

 ularly hexagonal or tetragonal in shape, and so closely crowded that the skin is entirely 

 concealed. 



Snout in front of orbits about 4.0 times as long as distance between orbits in young, 

 about 5.0 times in large females, and 4.5 times in large males; its length in front of 

 mouth about 3.1 times as great as width of mouth in young and 2.7—2.9 times in larger 

 specimens of both sexes. Horizontal diameter of eye about ^s as long as distance between 

 spiracles, or a little longer. Length of eye plus spiracle about ^U—*U ^^ great as distance 

 between spiracles. Spiracles about ^/j as long as orbit, nearly transverse, about -/j as 

 long as eyes; posterior margin with two well marked folds or ridges, the outer the 

 larger. First to fourth gill openings about equal in length, about 1/3 as long as nostril, 

 the fifth a little shorter; distance between inner ends of fifth gill openings 1.3— 1.5 times 

 as great as breadth of mouth. Nostrils moderately oblique, their length about as great 

 as distance between them or a little greater, and somewhat more than half (57-58 "/o) 

 as great as width of mouth; anterior margin expanded midway as a narrow lobe with 

 rounded tip, curving outward and across nasal aperture and extending inward a short 

 distance as a narrow fold that ends abruptly without encroaching on the internarial 

 space; margins of nostril about as in R. horkelii (p. 58) except that digitate flap of 

 posterior margin extends along nasal aperture about 70 "/o of distance toward inner 

 corner of nostril. Mouth nearly straight with slight bow centrally, its corners with 

 small wrinkles. Roof of mouth, close behind tooth-band, with a narrow transverse fold 

 that widens as a low rounded lobe on either side and extends the whole breadth of 

 mouth; its anterior surface sculptured with many low rounded prominences about 

 equal in size to the teeth, its free edge conspicuously fringed. 



Teeth in quincunx, 51^!^ in specimens 390—580 mm long, alike in form in the 

 two jaws and in the two sexes; closely crowded, rectangular to pentagonal basally, 

 with rounded corners, the functional surface a little elevated in subangular form along 

 the transverse axis; the younger rows with a low, blunt, conical cusp which is lacking 



