188 BULLETIN 36, UNITED STATES NATIONAL MUSEUM. 



Teeth ^, obliquely and often very irregularly' implanted, and of vary- 

 ing size. Vertebne: C. 7 ; D. 11; L. 9; Ca. 23=50. 



Eostrum of skull rather less than half the total length ; broad at the 

 base, tapering rapidly to the middle, but with the margins of the distal 

 half approximately parallel. Intermaxillte broad and moderately con- 

 vex, rarely extending backward to the posterior wall of the superior 

 nares. Expanded proximal portion of maxillic not bent upward as in 

 other dolphins, so that the entire upper surface of the skull is nearly in 

 one and the same plane. Pterygoid bones far apart at the base, con- 

 verging toward the extremity but not meeting; the sinus of very small 

 proportions. 



Measurements of the exterior. — Total length, 137.5 inches; tip of snout 

 to pectoral fin, 29 inches; length of pectoral fin, 1G.5 inches; greatest 

 breadth of pectoral fin, 10.5 inches; breadth of flukes, 



Measurements of the sJcull. — (No. 2958, K. Coll. of Surgeons, Lon- 

 don.) Total length, 55.3""; length of rostrum, 20.4""; breadth of ros- 

 trum at base, 18.3™; at its middle, 9.9'"; breadth between orbits, 27.2™; 

 length of temporal fossa, 15.2'"'. 



Habitat. — Arctic and sub-Arctic seas; north to 81° 35' (Grcely), 

 straggling southward to Firth of Forth, Scotland, and Cape Cod, Mas- 

 sachusetts. 



19. MOKODON Linne'. 



MONODON MONOCERAS Liuu6. 

 (Plate 47, ligs. land 2.) 



Head short and rounded. Pectoral fins short and broad. Dorsal fin 

 rudimentary; a low ridge. 



Color above dark gray or dusky ; below, white ; sides and back mot- 

 tled with gray. 



Teeth in the form of two spirally-twisted tusks, which are usually 

 concealed in the female; in the male the left tusk (rarely the riglit, or 

 both) is greatly developed. Vertebr;e: C. 7; D. 11 ; L. G; Ca, 20=50. 

 Cranial characters as in Delphinapterus. 



Measurements of the exterior. — (From Fleming.) Total length, 144 

 inches; tip of snout to pectoral fin, 30 inches; length of pectoral fin, 

 15 inches; greatest breadth of pectoral fin, inches. 



Measurements of the sA-m/L— (23455, U. S. Nat. Mus. 9 , with 2 tusks.) 

 Total length, 54""; length of rostrum, 23.7 '" ; breadth of rostrum at 

 base, 22""; at its middle, 13.7""; breadth between orbits, 34.4"^; length 

 of temporal fossa, 15.2"". 



Uabitat. — Arctic seas. 



