NO. 3537 SHARK GENUS ISURUS — GARRICK 681 



Trunk slender, its height at pectoral origin about one-seventh of 

 its length to subcaudal origin. Caudal peduncle notably flattened 

 dorsoventrally, and expanded laterally to form a sharp-edged hori- 

 zontal keel along midlevel of each side; anteriorly the keels become 

 inconspicuous a Httle behind tips of pelvic fins, while posteriorly they 

 extend onto anterior part of caudal fin. Lateral line not prominent. 

 Upper and lower precaudal pits strongly developed, their anterior 

 margins transverse and sharply defined. 



Dermal denticles small, close packed, overlapping, circular in out- 

 line, each with three longitudinal ridges and three posterior marginal 

 teeth, the latter relatively larger in denticles of smaller specimens, 

 median tooth always longer than lateral teeth. 



Head long, its length to fifth gill opening one-quarter of total length, 

 its greatest width 2.2 to 2.1 in its length. Snout sharply pointed, 

 conical, shghtly depressed dorsally, its length to eye 4.2 to 4.3 in 

 head. Prenarial length equal to internarial distance and 1.4 to 1.5 

 in preoral length. Eye large, circular, its diameter 2.8 to 3.1 in snout, 

 its anterior margin slightly behind front of mouth. Nostrils almost 

 transverse, small, their anterior margins with a low pointed lobe. 

 Mouth large, rather long, upper Hp broadly arched at front, lower lip 

 not meeting upper even when mouth is closed; width of mouth 1.2 in 

 its length. Labial furrows long, upper more than one-third length of 

 mouth, lower about two-thu-ds as long as upper. Gill openings very 

 large, their vertical lengths extending almost two-thirds of depth of 

 body at same region; lower end of fifth gill opening extends beneath 

 and slightly behind pectoral fin origin. 



Teeth ^^ o^ ^^"^^ ^^ |^ ^ similar in upper and lower jaws, unicusped, 



narrowly triangular, smooth edged, with complete cutting edges on 

 then- lateral and medial margins; first two teeth on each side of sym- 

 physis in both jaws noticeably longer than others; those in upper jaw 

 closely followed by a very much smaller third tooth, and the latter by 

 a distinct gap before larger lateral teeth begin; first two upper teeth 

 sUghtly oblique to curved in outline; in side view these first two upper 

 teeth are virtually straight except for their tips which curve outward; 

 lateral teeth obhque in outhne, and progressively smaller toward 

 angles of jaws. In lower jaw the third tooth smaller than first two 

 teeth but at least as large as fourth, and the gap between thu-d and 

 fourth teeth not greater than that between fourth and fifth; first lower 

 tooth distinctly narrower than second; first two lower teeth weakly 

 flexuous in outline ; in side view the first two lower teeth are curved in- 

 ward except for their tips which are reverse curved Uke those of upper 

 teeth; lateral teeth obUque and diminishing in size toward angles of 

 jaws. Two or three rows of teeth functional at center of mouth in both 

 jaws, one or two rows along sides. 



