668 TELEOSTEI CHAP. 
An Atlantic species of Hphippus (#. faber) is extremely 
remarkable, when adult, for an enormously enlarged globular 
bony mass on the back of the head, formed by hypertrophy of the 
frontal and supraoccipital bones. 
Principal genera: EHphippus, Parapsettus, Scatophagus, Chae- 
todon, Chelmo, Heniochus, Holacanthus, Pomacanthus, Plataz. 
Chaetodon, Holacanthus, Pomacanthus, Scatophagus, Ephippus, 
and Platax were represented in the Eocene of Europe. 
Fam. 28. Drepanidae.—The genus Drepane, with a single 
species from the Indian Ocean, is very closely related to the 
Chaetodontidae, but it lacks the subocular shelf, and it is distin- 
guished externally by the very elongate, falciform pectoral fin. ' 
Fam. 29. Acanthuridae.—A more or less developed sub- 
ocular shelf; entopterygoid present. Mouth very small, not or 
but slightly protractile, the maxillary more or less firmly attached 
or ankylosed to the praemaxillary ; teeth conical, bristle-like, or 
incisor-like. Palate toothless. Vertebrae 22 or 23, the prae- 
caudals with strong transverse processes commencing from the 
first; ribs and epipleurals inserted on the transverse processes. 
Post-temporal not distinctly forked, ankylosed to the skull. Two 
nostrils on each side. Gill-membranes broadly attached to the 
isthmus; 4 or 5 branchiostegal rays; gills 4,a slit behind 
the fourth ; pseudobranchiae present. Lower pharyngeal bones 
separate. Body covered with minute, often rough scales. ~ Dorsal 
and anal fins elongate, with more or less strong spines. Ventrals 
with 1 spine and 2 to 5 soft rays. 
A family of about 80 species, mostly herbivorous, from the 
tropical seas, referred to 6 genera : Zanclus, Ctenochaetus, Acan- 
thurus, \Colocopus, Prionurus, Naseus. They form a connecting 
link between the Chaetodontidae and the Plectognathi. 
Remains from the Eocene of Europe have been referred to 
Zanclus, Acanthurus, and Naseus, and to the extinct genera 
Aulorhamphus and Apostasis. 
Fam. 30. Teuthididae.—No subocular shelf; entopterygoid 
present. Mouth very small, beak-like, not protractile, with 
incisor-like teeth; maxillary ankylosed to the praemaxillary. 
Palate toothless. Two nostrils on each side. Gill-membranes 
broadly attached to the isthmus; 5 branchiostegal rays; gills 
4,a slit behind the fourth; pseudobranchiae present. Lower 
pharyngeal bones separate. Supratemporal forked. Vertebrae 
