246 Memoir Sears Foundation for Marine Research 



areas of skin visible between, the blades nearly horizontal, on short pedicels, lanceolate, 

 strongly sculptured with 2 to 6 longitudinal ridges, the median pair flanking the axis of the 

 blade and usually extending out to its extreme tip, the basal part so opaque that the pedicel 

 is not visible from without, even in fresh specimens, their margins usually entire but some- 

 times weakly notched between the tips of the ridges, and often irregularly worn. 



Head flattened above, its dorsal outline nearly straight, sloping to thin-tipped snout. 

 Snout broadly ovate at tip, its length in front of mouth a little greater than Ys the length 

 of head to origin of pectoral. Eye oval, its horizontal diameter slightly shorter than dis- 

 tance between nostrils, the subocular fold separate at both ends from the margin of the 

 lower eyelid in small specimens, but joining the latter at the anterior corner of the eye 

 by the time a total length of about 700 mm. is reached 5 in very large specimens it becomes 

 continuous with the margin of the upper lid at both corners. Spiracle oval, about Ve to Yi 

 as long as horizontal diameter of eye, about on a level with center of latter and behind it 

 by a distance V2 as long as horizontal diameter of eye. Third and fourth gill openings 

 slightly the longest, about i Ys times as long as horizontal diameter of eye, the 5th con- 

 siderably the shortest, their outlines nearly straight or weakly concave anteriorly, the 5th 

 the most so, the 4th gill opening above origin of pectoral. Nostril about as long as hori- 

 zontal diameter of eye, oblique, its inner corner about Ys as far from front of mouth as 

 from tip of snout, its anterior margin expanded as a well developed subpentagonal lobe 

 with blunt tip. Mouth occupying between Y2 and % of breadth of head, ovate, about twice 

 as broad as high. A strongly marked labial furrow on each jaw, the upper usually consider- 

 ably the longer in northern specimens, but sometimes only about as long as the lower, or 

 even slightly shorter, in West Indian and South American races.^ 



Teeth ^ in specimen counted, usually 5 to 7 rows functional, the cutting edges with 

 bluntly rounded apices directed somewhat outward {i.e., asymmetrical), their margins 

 slightly concave (the outer usually the more deeply so) or sometimes even notched, espe- 

 cially in small specimens. 



First and second dorsals similar in shape, with very slightly convex or nearly straight 

 anterior margins, narrowly rounded apices, deeply concave rear margins and acute rear 

 corners, the free lower edges about Ys as long as the bases. Origin of ist dorsal about over 

 midpoint of inner margin of pectoral, the midpoint of its base about as close to axil of pec- 

 toral as to origin of pelvics. Second dorsal nearly or quite as long as ist at base, but only 

 about % to % as high, its origin at a perpendicular about midway between tips of pelvics 

 and origin of anal, its rear tip a little anterior to rear tip of anal. Caudal about Yo of total 

 length, with truncate tip, the terminal sector noticeably large or a little more than Vs of 

 total length of caudal, with well marked subterminal notch, the lower anterior contour 

 expanded as a low but well marked lobe, with broadly rounded apex. Anal only about % 

 as long at base as 2nd dorsal, and about Y2 as high, with less deeply concave posterior mar- 

 gin and shorter free rear corner, its origin about under midpoint of base of 2nd dorsal. 



7. See Bigelow and Schroeder, Proc. Boston Soc. nat. Hist,, ^i (8), 1940: 422. 



