24. CIIBLERIDyE. 53 



margins of the disk darker. (Dumeril.) Tropical waters of A.nierica; 

 north to North Carolina and San Diego. Keaches a width of about 20 

 feet. 



("Raia lirostris Walbaum " : Cephaloptmt vampyrus Mitchill, Ann. Lye. Nat. Hist. N. 

 Y. 1823, 23: Diabolichthys eUiotli Holmes, Proc. Elliott Soc.Nat. Hist. 1856, 39: Ceratop- 

 tera vampyrus Duin6ril, Hist. Nat. Poiss. i, 6GO : Cerutoptera vampyrus Giintlier, viii, 498.) 



SUBCLASS HOLOCEPHALI. 



(The Chimceras.) 

 The characters of the single order. 



ORDER F.-HOLOCEPHALL 



(The Chimceras.} 



Skeleton cartilaginous. Gill-cavity with four clefts within, but having 

 one external opening only, which is covered by a fold of skin, within 

 which is a rudimentary cartilaginous operculuin. No spiracles. Mouth 

 inferior. Jaws without separate teeth, but armed with bony plates. 

 Intestines with a spiral valve. No air-bladder. Jaws and palate 

 coalesceut with the skull. Derivative radii sessile on the sides of the 

 basal bones of the limbs, separated from the articulation. Pectoral fins 

 normally developed, placed low. Yentral fins abdominal. Tail taper- 

 ing. Skin smooth or nearly so ; its muciferous system well developed. 

 A single family. 



(Holocephala GUutber, viii, 348-352; o/lof, solid; Ketyafa], head.) 



FAMILY XXIV. CHIM^RUX^E. 



(The Chimceras.) 



Body elongate, rather robust anteriorly, tapering posteriorly. Head 

 compressed. Mouth inferior. Upper lip deeply notched. Nostrils 

 confluent with the mouth, separated by a narrow isthmus. Jaws with 

 the teeth confluent into four bony laminae above and two below. No 

 spiracles. Males with a peculiar cartilaginous hook, armed with prickles 

 at the tip, and turned forward on the upper part of the snout. Pectoral 

 fins free, placed low. Ventral fins abdominal, many-rayed, provided in 

 the male with claspers. Dorsal fin usually divided ; anteriorly with a 

 very strong spine, which is grooved behind. Caudal fin low, fold-like- 

 Skin naked, rarely somewhat prickly. Lateral line present, usually 

 with numerous branches anteriorly. Three free gills and two half gills, 



