Jordan and Evermami. Fishes of North America. 605 



291. IDIACANTHUS, Peters. 



LKacanttius, PETERS, Monatsber. Akad. Wies. Berlin, 1876, 846, (fasciola). 

 BatlujopMs, Gi : NTHER, Ann. Mag. Nat. Hist., 1878, 181, (ferox). 



Body snake-like, very slender and elongate, scaleless. Vent very far 

 back. Head large, compressed, the snout moderate, the cleft as long as 

 head. Teeth extremely large, numerous, unequal, fang-like, depressible, 

 present on jaws, vomer, and palatines. Eye small; opercles narrow. 

 Hyoid bone with a long barbel. Dorsal long and very low, extending 

 from above ventrals nearly to caudal ; the rays simple, each one placed 

 behind a pair of spine-like processes; no adipose tin; no pectorals; ven- 

 trals median. A luminous organ above middle of upper jaw and a series 

 of luminous dots along side of belly and on outer ray of ventral and on 

 tail. Gill openings very wide; branchiostegals short, numerous. Gills 

 4; no pseudobranchi*. Vertebrae numerous, 67 in Idiacanthus ferox. Three 

 species known. (Idtos, peculiar; a/cavfla, spine.) 



a. Dorsal fin inserted opposite root of ventrals; anal rays 45. FEROX, 903. 



au. Dorsal fir. inserted well in advance of ventrals; anal rays about 35. ANTROSTOMUS, 904. 



903. IDIACANTHUS PEROX (Gunther). 



D. 60 ; A. 45 ; V. 6. Vertebra) 67. Vent in sixth eighth of total length. 

 Dorsal inserted opposite ventrals. Color black. North Atlantic, nearly 

 midway, in 2,750 fathoms. One specimen, 8 inches long. (Gunther.) 

 (ferox, fierce.) 



Bath yophis ferox, GUNTHER, Ann. Mag. Nat. Hist., n, 1878, 181, North Atlantic. 

 Idiacanthus ferox, GUNTHER, Deep-Sea Fishes Challenger, xxn, 216, 1887. 



904. IDIACANTHUS ANTROSTOMUS, Gilbert. 



Head 12; depth 16. D. 57; A. about 35. Abdomen much dilated, 

 abruptly constricted immediately behind the ventral fins, and much nar- 

 rowed anteriorly, the depth again increasing to occiput. Greatest depth 

 immediately in front of veutrals. Maxillary reaching edge of gill cover. 

 Teeth in a single series in each jaw, readily depressible, varying greatly 

 in length ; teeth in the upper jaw arranged in groups of 4 or 5, the 

 anterior member of each group being very short, the others rapidly 

 increasing backward, the posterior tooth very long ; lateral teeth in 

 mandible inserted at the extreme outer edge of the jaw, the anterior teeth 

 inserted farther inward; thus the last of the anterior teeth are distinctly 

 within the first of those on sides of jaw ; a single small tooth on each 

 side of vomer, and 2 or 3 posteriorly on palatines ; 3 pairs of teeth 

 directed backward from near tip of tongue. Eye over first third of 

 length of maxillary ; lower jaw much longer than the upper. Barbel i 

 longer than the head, expanded near its tip, and again narrowed as in I. 

 ferox. Dorsal beginning well in advance of ventrals, its distance from 

 tip of snout 3 in total length; anterior rays distant, the membrane 

 from one ray reaching only to basal portion of the succeeding ray ; each 

 ray starting behind a pair of short spinous projections which diverge back- 

 ward, the fin when depressed lying in the groove formed by these diverg- 

 ing pairs of spines ; caudal forked, the rudimentary rays extending well 



