46 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
times length of snout; pectoral, when depressed, reaching to a vertical through posterior edge of base 
of dorsal, the tip bluntly pointed; edges of pectoral and. first dorsal concave, that of second dorsal 
emarginate; edge of ventrals straight; distance from anterior edge of anal opening to tip of depressed 
ventral 2.4 in head; upper caudal lobe 3.7 in its length; a low lateral keel on caudal peduncle. 
Color, dark slaty blue above, lighter below. 
Some of the specimens examined have the head slightly narrower than examples of the same 
species from Japan, while others are like them in every particular. 
Squalus mitsukurU Jordan & Snyder, Proc. U. S. Nat. Mus., XXVI, 1903 (Mar. 30), 629, fig. 3, Misaki (Type, No. 718-1, 
Stanford Univ.); Snyder, Bull. U. S. Pish Comm., XXII, 1902 (Jan. 19, 1904), 515 ( Albatross Station 4085, oft' north 
coast of Maui). 
Genus 12. ETMOPTERUS Rafinesque. 
Mouth little arched; teeth of lower jaw with the point so much turned aside that the inner 
margin of the tooth forms the cutting edge; upper teeth erect, each with a long pointed cusp and one 
or two smaller ones on each side; spiracles wide. 
Of the 2 known species one occurs in Hawaiian waters. It is described in Section II of this work. 
Elmopterus Rafinesque, Caratteri, etc., 14, 1810 ( aculeatus ). 
Spinax Cuvier, ROgne Animal, Ed. I, 129, 1817 ( acantliias and spinax). 
Spinax Muller & Henle, Plagiostomen, 86, 1838 {spinax). 
Acanthidium Lowe, Proc. Zool. Soe. London 1839, 91 (pusillum). 
Genus 13. CENTROSCYLLIUM Mtiller & Henle. 
Teeth equal in both jaws, very small, straight, pointed, each with 1 or 2 smaller cusps on each 
side at base; mouth crescent-shaped, with a straight, oblique groove at its angle; spiracles moderate; 
gill-openings rather narrow; dorsal fins small, each with a strong spine; the second dorsal entirely 
behind the ventrals. One species in the Arctic Seas and another recently discovered by the Albatron s 
off Ivauai. The latter is described in Section II. 
Centroscyllium Muller & Henle, Plagiostomen, 191, 1838 (fabricii). 
Order D. BATOIDEI. — The Rays. 
Gill-openings 5, slit-like and inferior; spiracles present; no anal fin; dorsal fins, if present, 
inserted on the tail; body typically disk-like, broad and flat, the margin of the disk being formed by 
the expanded pectorals; tail comparatively slender, the caudal , fin small or wanting; vertebrse 
cyclospondylous. With the exception of the Rajidse, most or all of the rays are ovoviviparous. 
a. Pectoral fins uninterrupted, confluent around the snout; teeth small Dasyatidx, p. 16 
aa. Pectoral fins interrupted, one portion forming detached appendages, or “cephalic fins,” on the snout. 
b. Teeth very large, flat, tesselated, few in number Aetobatidx, p. 48 
bb. Teeth very small, flat, or tubercular, numerous; cephalic fins conspicuous, resembling horns; size enormous. 
Mobulidse, p. 50 
Family VIII. D ASY ATI DT. — The Sting Rays. 
Disk usually more or less broad than long; pectoral fins uninterruptedly confluent in front, 
forming the tip of the snout; tail variously formed, usually whip-like, sometimes short and stout, 
sometimes bearing a single dorsal or caudal fin, but never with 2 dorsals; usually one or more vertical 
folds of skin on the tail, rarely a lateral fold; tail generally armed with a large, sharp, retrorsely 
serrate spine on its upper surface toward the base; 2 or 3 spines occasionally present; ventral fins 
not emarginate; skin smooth or variously prickly or spinous, roughest in the adult; no differentiated 
spines on the pectorals in the males, the sexes similar; mouth rather small; teeth small, paved, 
usually more or less pointed or tubercular; nostrils close together, nasal valves forming a rectangular 
flap, which is joined to the ujrper jaw by a narrow frenum; spiracles large, placed close behind the 
eyes; skull not elevated, the eyes and spiracles superior. Ovoviviparous. Genera about 10; species 
