368 Memoir Sears Foundation for Marine Research 



thence rearward over a zone of considerable breadth to a little in advance of the pelvic 

 girdle, where the zone thus roughened narrows abruptly onto the base of the tail. Tail 

 posterior to spine rather sparsely strewn with smaller sharper thorns or large prickles 

 from upper side down to lower side. Lower surface of disc and of anterior part of tail 

 smooth at all stages of growth. 



Snout in front of eyes about 1.4 times as long as distance between outer margins 

 of orbits, its length in front of mouth about 2.7—2.9 times as great as distance between 

 exposed nostrils and 1.4— 1.5 times as great as distance between inner ends of first gill 

 openings. Distance between inner ends of first gill openings about 1.8— 2.1 times as 

 long as distance between exposed nostrils; distance between inner ends of fifth gills 

 60-70 "/o as long as that between first gills. Posterior margin of nasal curtain nearly 

 straight or weakly concave, fringed with short lobes, simple or bifid and rounded at 

 tip. Upper jaw strongly arched forward but projecting a little rearward centrally, the 

 lower jaw weakly recessed to correspond. Floor of mouth centrally with three stout 

 papillae in transverse series. 



Teeth f^^; those of females and immature males tetragonal with rounded corners, 

 the functioning surface weakly arched or flat and often ridged by wear, the uppers 

 largest about midway between center of jaw and outer corners, the lowers about uni- 

 form in size all along jaw except near outer corners where somewhat smaller; 6-7 rows 

 in function simultaneously in upper jaw, 8—9 rows along central part of lower jaw, 

 6—8 rows toward outer corners. Teeth of mature males not seen. 



Pelvics ovoid, reaching rearward only a little beyond posterior corners of pectorals ; 

 their outer and posterior corners well rounded, with posterior and inner margins merg- 

 ing in evenly convex contour; anterior margin about 90— iio^o ^s long as distance 

 from its own origin to rear tip of longest ray of pelvic. Claspers of mature males not seen. 



Color. Recently caught specimens (not seen by us) are described as having upper 

 surface brown, sometimes yellowish or olivaceous, either plain or with darker spots, or 

 uniform pale gray. Lower surface pure or yellowish white; ventral tailfold and dorsal 

 keel black. 



Size. This has long been known as one of the larger members of its genus. An 

 early account "^ credits it with a width up to five or six feet and a tail up to 1 1 feet long, 

 while the claspers of a male about 450 mm wide were still rudimentary. The size at 

 birth is not definitely known, but probably it is somewhat greater than 150 mm, for 

 embryos up to 133 mm broad in our Study Material (p. 365) still bear small yolk sacs. 



'Developmental Stages. Embryos 103—133 mm wide with yolk sac still attached 

 (see Study Material) resemble their parents closely in form of disc and in having the 

 lower tailfold already formed though narrower. However, their skins are perfectly 

 smooth (p. 367), while their tails are slightly longer relatively (about 2.7 times as long 

 as disc) and hair-fine toward the tip. 



The number of young that a female may set free at one time has not been recorded, 

 but it is likely that six embryos in the Harvard Museum of Comparative Zoology may 



105. Bloch and Schneider, Syst. Ichthyol., 1801: 361. 



