150 Memoir Sears Foundation jar Marine Research 



Head slightly compressed laterally opposite mouth (strongly so in small specimens). 

 Snout very short, subconical, with rounded tip in larger specimens but relatively much 

 longer in small ones, forming a subcylindrical proboscis, obliquely truncate in front, 

 terminating dorsally in a sharp point, with many circular pores on its dorsal surface; transi- 

 tion from the juvenile to the adult form takes place at lengths of 1 2 to 1 6 feet. Eyes nearly 

 circular without nictitating membrane or subocular folds, their diameters only about Vs 

 as great as distance between them opposite, or a little posterior to, front of mouth. Spiracles 

 described as minute, circular, a little posterior to angles of jaws or opposite latter. Gill 

 openings very large, extending from upper sides down onto lower surface of throat, the 

 1st longest, the 5th shortest, the ist pair separated below by 6 inches only, the 2nd pair 

 by 9 inches, the 4th pair by 21 inches and 5th pair by 27 inches in a specimen" 30 feet 3 

 inches long. Gill rakers very numerous (about 1,260 on gill studied), flattened basally on 

 the adjacent sides but bristle-like toward the tips, in a continuous series, and directed in- 

 ward; I series on the ist gill arch, 2 series on the 2nd, 3rd and 4th and only i series 

 described for the 5th." Nostrils wide apart at outer edges of snout, small, transverse, con- 

 siderably nearer to mouth than to tip of snout in young specimens, less so in adults because 

 of decrease in relative length of snout, their anterior margins slightly expanded in sub- 

 triangular outline. Mouth very large, occupying most of breadth of head, rounded in 

 adult but varying in young from nearly transverse, with corresponding lateral expansion 

 of sides of head behind the eyes, to broadly V-shaped; these variations probably associated 

 with wide distensibility of mouth and loose articulation at symphyses. A very short labial 

 furrow at corner of mouth on lower jaw, but none on upper. 



Teeth minute, being only about 3 mm. high in specimen about 12 feet 9 inches (3,900 

 mm.) long and about 6 mm. in one of 30 feet; in 4 to 7 functional series, with lOO or more 

 teeth in each row on each side of jaw; those toward center of mouth low and triangular, 

 but those along the sides conical, slightly recurved, somewhat compressed laterally, with a 

 ridge on each side, the basal part striated ; a wide space with only scattered teeth at center 

 of upper jaw (106 mm. wide in 12-foot specimen) but not of lower jaw. 



First dorsal fin an approximately equilateral triangle, its anterior margin nearly 

 straight, its posterior margin slightly concave or even slightly convex in some cases, its 

 apex subacute, its free rear corner extending only a slight distance beyond the rear termina- 

 tion of its base, the height along anterior margin varying from about 1 1 to 14% of total 

 length, its origin considerably behind the inner corner of the pectoral when latter is laid 

 back; the midpoint of its base about midway between tip of snout and fork of caudal. 

 Second dorsal's anterior margin only ^/4 to Vs as high as ist, with rounded apex, strongly 

 concave rear margin and free rear tip about as long as its base. Caudal ^^ to Vs of total 

 length, lunate, its axis steeply raised as in Isuridae, its posterior outline obtusely sub- 

 angular rather than rounded, with well marked subterminal notch, its lower anterior 



11. Storer, Mem. Amer. Acad. Arts Sci., (2) p, 1867: 229. 



12. See White (Bull. Amer. Mus. nat. Hist., 7^, 1937 : pis. 7, 8) for photographs of gill rakers in position. 



