ACANTHIDIUM. 215 



ACANTHIDIUM. 



Acanthidium Lowe, 1839, Proc. Zool. soc. London, p. 92; 1843, Trans. Zool. soc. London, 3, p. 18. 

 Deania Jord. & Snyder, 1902, Proc. U. S. nat. mus., 25, p. 80. 

 Nasisqualus Smith & Radcliffe, 1912, Proc. U. S. nat. mus., 41, p. 681. 



Body elongate, subfusiform, slightly compressed. Head depressed; snout 

 very long, longer than the remainder of the head, spatuliform, blunt; nostrils 

 in front of the middle, transverse. Mouth behind the mid length of the head, 

 with a deep groove and with labial folds at each angle. Teeth compressed, tri- 

 angular, sectorial, diverse, cusps erect to very oblique. Eyes large, no nictitating 

 membrane. Spiracles large, superior, behind the eyes. Gill openings narrow, 

 in front of the pectoral. Pectorals moderate, not produced on the inner angle. 

 Two dorsals, each with a compressed spine each side of which bears a groove; first 

 dorsal above the space between pectorals and ventrals, second behind the ventrals. 

 No anal fin. Tail much shorter than the body ; lower lobe of caudal hardly pro- 

 duced. Scales very small, each with a slender peduncle on a broad polygonal or 

 radiating base and crowned with three (3-4) slender acuminate cusps. 



Species now known from the Northern Atlantic, the Mediterranean, and 

 Japan. 



Lowe, 1839, characterized this genus and placed within it two species, A. 

 pusillum and A. calccus. As A. pusillum properly belonged to Etmopterus 

 Rafinesque, 1810, A. calceus was really the typical and for many years the only 

 known species of the genus. 



First dorsal spine equidistant from end of snout and caudal 

 bases of the two dorsals about equal 



eye nearer to end of snout than to pectoral 



teeth cusps near symphysis of lower jaws subhorizontal 



calceus (page 216) 

 base of first dorsal much longer than that of second 



teeth near symphysis of lower jaws with erect cusps 



aciculatum (page 217) 

 First dorsal spine nearer to end of snout than to caudal 

 eye nearer to end of snout than to pectoral 



teeth near symphysis of lower jaws obhque on cutting edges 

 inner angle of pectoral longer 



spine of dorsal behind ends of pectorals 



rostratum (page 218) 

 spine of dorsal above ends of pectorals 



profundorum (page 219) 



