252 



BULLETIN OF THE BUREAU OF FISHERIES. 



Genus APRIONODON Gill 

 9. Aprionodon isodon (Miiller and Henle). 



Aprionodon isodon, RadcUffe. 1914, p. 414. 



Teeth. — Teeth in |-^ rows, small, erect, compressed, without serrations; cusps nairow, sharp-pointed; 



bases broad, forming a distinct shoulder; three rows of minute 

 teeth at symphysis of upper jaw; a median row of minute 

 teeth at symphysis of lower jaw, a row on either side of it of 

 smaller teeth than those which follow; lower teeth smaller than 

 the upper. 



Denticles. — The dermal denticles.are very thin and small, 

 being about 0.27 mm. long by 0.28 mm, broad in a shark 50.8 

 cm. in length, three-keeled, imbricated, outer surface relatively 

 flat, keels low, parallel; apical margin normally with three 

 sharp-pointed lobes, the number varying from three to five, 

 median lobe longest, incision between lobes sharp-cut, relatively 

 deep; in many of the denticles these lobes are broken or worn 

 away; basal margin rounded; pedicel short, stout; base large, 

 stellate. The denticles of this species differ from those of 

 Scoliodon terrcE-novtE in being more closely imbricated, slightly 

 larger, with weaker keels, lobes of apical margin sharper and 

 longer, three to five in number, pedicel shorter and stouter. 

 The laboratory' collections at Beaufort contain a single exam- 

 ple of this species 50.8 cm. (20 inches) in length, for which there is no record as to date or method of 

 capture. 



Measurements of this Example, a Female. 



Fig. 9. — Teeth. Aprionodon isodon, 50.8 cm. 

 long, in Beaufort collection. (Same speci- 

 men as fig. 10.) 



Total length 



Tip of snout to — 



Origin of dorsal 17. 



Anterior margin of eye 4. 



First gill slit 10. 



Last gill slit 



Base of pectoral 12 



Front of mouth 3, 



Outer angle of nostrils 2. 



Horizontal diameter of orbit 



Vertical diameter of orbit o. 



Distance between nostrils 2. 



Length of nasal aperture o. 



Distance between angles of mouth 4 



Height of— 



First gill slit 2 



Second gill slit 2 



Third gill slit 2. 



Fourth gill slit 2, 



Fifth gill slit 2 



Length of anterior margin of first dorsal. . . 6. 



cm. 



50.8 



Length of posterior margin of first dorsal 2. 2 



Base of first dorsal 5. o 



Distance between dorsals 10. o 



Length of anterior margin of second dorsal 2.5 



Length of posterior margin of second dorsal , , 2.2 



Base of second dorsal 2.2 



Length of outer margin of pectorals 7. 5 



Length of inner margin of pectorals 2.7 



Breadth of pectoral 4. 5 



Axil ol pectorals to base of ventrals 9. 5 



Length of outer margin of ventrals 2.9 



Length of inner margin of ventrals 2.9 



Breadth of distal margin of ventrals 2. 7 



Length of anterior margin of anal 3.1 



Length of posterior margin of anal 2. 2 



Base of anal 2. 3 



Axil of anal to origin of lower caudallobe ,.*.*.. 3.7 



Length of upper caudal lobe 14. i 



Length of lower caudal lobe 5.9 



Tip of caudal to notch 3.8 



Breadth of tip of caudal lobe 3. ^ 



Snout short, depressed, blunt, its length about equal to breadth of mouth; nostrils small, with 

 a short, rounded, flaplike projection near inner angle, length of aperttu-e equal to vertical diameter 

 of orbit; distance from tip of snout to outer angle of nostrils, one-half distance from angle of nostril 

 to angle of mouth; mouth large, distance from tip of mandible to angle slightly less than distance be- 

 tween angles. An eye diameter behind eye, there is a porelike aperture which resembles a rudi- 

 mentary spiracle. Gill slits elongate, the third longest, 2.8 times horizontal diameter of eye; fifth 

 shortest, above pectoral base. 



First dorsal high, nearer base of pectorals than ventrals, distal margin concave, anterior lobe 



