392 Memoir Sears Foundation for Marine Research 



increasingly obtuse with growth until nearly straight across; outer and posterior cor- 

 ners broadly rounded; posterior margins moderately and evenly convex, the inner 

 margins somewhat more strongly so. Axis of greatest breadth 44—49 "/o of distance 

 rearward from tip of snout toward rear limits of disc. Tail from center of cloaca i .8— 2.0 

 times as long as body from cloaca to tip of snout; moderately stout anterior to spine,!^* 

 rounded above but only weakly rounded or even flat below on small specimens; narrow- 

 ing to a whiplash tip; approximately circular in cross section posterior to spine; either 

 side with a low and obscure longitudinal ridge extending from about opposite tips of 

 pelvics to about half the distance toward spine; lower surface of tail with a low ridge 

 extending from below origin of spine past tip of latter for a short distance. 



Tail spine originating posterior to center of cloaca by a distance nearly as long 

 as distance from cloaca to tip of snout; free portion of tail spine, when fully developed, 

 about 1. 0—1.4 times as long as distance between outer margins of orbits, its total 

 length from origin about 1.3— 1.7 times; its maximum breadth 5.0—6.5 "/o ^s great as 

 its total length; only one spine on specimens seen but preceded in each case by a well 

 mended scar, suggesting that the present functional spine is a replacement; hence 

 two may be expected on some specimens ;i" marginal teeth about 70 on specimen 

 counted,!^* of the shape shown in Fig. 94 C, so close together as to form a nearly con- 

 tinuous cutting edge. 



Entire upper surface of disc and of tail back to spine rather closely and evenly 

 set with small, low, blunt tubercles, quadriradiate in form, each of the basal radii branch- 

 ing dichotomously (Fig. 94 D); most closely crowded and largest over midbelt of disc 

 and on root of tail, smaller to minute along margins of disc and rearward along tail 

 posterior to spine; one similar but much larger tubercle on each shoulder on small 

 specimens, two or more on larger; pelvics smooth. Lower surface of disc perfectly 

 smooth; pelvics also smooth below; lower surface of tail smooth below anterior to tip 

 of spine but sparsely and irregularly set thence rearward with minute quadriradiate 

 tubercles or prickles,i^' some blunt but others more thorn-like. 



Snout in front of orbits about i. 0—1.3 times as long as distance between outer 

 margins of orbits, its length in front of mouth about 2.0—2.6 times as great as distance 

 between exposed nostrils and 0.8-1. i times as great as distance between inner ends of 

 first gill openings. Orbit about 46 "/(, as long as distance between orbits in small 

 specimens but 27 "/o on the large one examined, and about 52-60 "/o as long as spiracle. 

 Distance between inner ends of first gill openings about 2.5—2.8 times as long as 

 distance between exposed nostrils; distance between inner ends of fifth gills about 

 70—80 "/o as long as that between first pair. Posterior margin of nasal curtain nearly 



156. The anterior parts of the tails of the preserved specimens we have seen show a more or less definite groove along 

 the midline, but we suspect that this is the result of muscular contraction rather than a normal characteristic of this 

 species. 



157. Two spines have been recorded for H.pacifica, a close ally. See Beebe and Tee-Van (Zoologica N. Y.,26, 1941: 

 263). 



158. Extreme tip broken off. 



159. One of the smaller specimens studied by us has only a few of these scattered here and there on the posterior part 

 of the tail, though it is in good condition otherwise. 



