130 Memoir Sears Foundation for Marine Research 



of trunk (not appreciably recurved). Tail from center of cloaca about as long as dis- 

 tance from center of cloaca to tip of snout on small specimens but a little longer rela- 

 tively in adults; rounded above, moderately flattened below; sides of tail evenly rounded 

 in small specimens (at least in most cases), but each with a low dermal ridge in adults 

 from about opposite origin of first dorsal to origin of caudal. 



Snout anterior to spiracles about twice as long as breadth between spiracles, its 

 length in front of mouth about 2.5 times as great as distance between outer ends of 

 nostrils. Eyes separated from spiracles by a distance about equal to length of latter; 

 minute, apparently nonfunctional, entirely covered over with skin and thus largely 

 concealed in small specimens and in some mature ones, but exposed as dark dots up 

 to one mm in diameter on other large specimens. Spiracles transverse or slightly oblique, 

 about ^li—^U ^s long as distance between them, rounded posteriorly when expanded, 

 their margins perfectly smooth. A pair of small mucous pores on nuchal region visible 

 under a lens. All gill openings about as long as spiracle; distance between inner ends 

 of first pair about 1.6 times as long as distance between spiracles; distance between 

 inner ends of those of fifth pair about 65—72 "/o as great as that between first pair. 

 Exposed portions of nasal apertures minute (even smaller than in Narcine) ; the isthmus 

 separating their inner ends (visible only when nasal curtain is lifted) about half as broad 

 as mouth when latter is retracted and closed (thus broader relatively than in N. bra- 

 siliensis)\ nasal curtain thick, fleshy, about V4 ^s long as broad, its free margin with 

 three low rounded expansions of about equal lengths; outer part of rear margin of 

 nostril expanded as a low, rounded, fleshy lobe directed inward toward isthmus between 

 both nostrils. Mouth with thick, wrinkled lips and surrounded by a deep moat; about 

 'V3— V4 as wide as distance between spiracles when retracted and closed; forming a short 

 tube (8 mm long in a 220-mm specimen) when protracted and opened. Tooth bands 

 occupying ^U—^U of breadth of mouth. 



Teeth j| to ^; closely crowded in quincunx arrangement, the bases subquadran- 

 gular; those of the younger series with a single slender cusp blunted at tip, directed 

 rearward into the mouth; those of older series (exposed when mouth is closed) with 

 cusps partly or wholly worn down; about seven rows in function simultaneously along 

 centers of tooth bands, four to five rows toward outer extremities. 



Dorsals approximately equal in size and similar in shape; anterior margins strongly 

 sloping; posterior margins weakly convex or nearly straight, recurving a little basally 

 in young specimens but hardly so in adults; apex rounded narrowly; base a little less 

 than */« (about 70 "/o) as long as anterior margin; vertical height a little less than length 

 of base. Origin of first dorsal anterior to rear tips of pelvics by a distance about 7$ 

 as long as base of first dorsal in young and in mature females; its position relative to tips 

 of pelvics not known for mature males. Interspace between dorsals about Vs as long 

 as base of first dorsal in adults but only about half as long in young. Interspace between 

 second dorsal and caudal varying from Vs ^^ about as long as base of second dorsal. 

 Caudal ovoid, its lower-posterior margin forming a continuous curve without inter- 

 rupting corner; upper margin less strongly convex; tip well rounded in small specimens 



