XXII ACANTHOPTERYGII 691 
Division VI.—DISCOCEPHALI. 
Highly aberrant Acanthopterygians with the anterior dorsal 
fin modified into a suctorial, transversely laminated oval disk? 
on the head, the skull being very much flattened and with simple 
basis cranii. The pectoral rays are inserted on the small, per- 
forate, scapula and on four hour-glass-shaped pterygials, three 
of which are in contact with the coracoid. Ventrals thoracic. 
Fam. 1. Echeneididae—Maxillary slender, adnate to the 
upper surface of the praemaxillary; suborbital arch slender. 
Pectoral fin inserted high up; supraclavicle much reduced ; 
ventral fin with one spine and five soft rays. Body elongate 
and covered with small scales; soft dorsal and anal fins elongate 
and apposed to each other. All the praecaudal vertebrae with 
very strong parapophyses, the anterior with diapophyses as well ; 
ribs and epipleurals nearly equally developed, both inserted at 
the extremity of the parapophyses. 
Fic. 421.—Remora brachyptera. (After Goode.) x 4. 
In spite of a superficial external resemblance to the genus 
Elacate, the Sucking-Fish bear certainly no affinity to that genus 
nor to other Scombriformes, as first observed by Gill. They are 
probably derived from Perciformes, but from which family it is 
impossible to suggest. Three genera may be distinguished: 
Opisthomyzon, from the Upper Eocene of Switzerland, with a 
very small suctorial disk and 235 or 24 vertebrae ; Heheneis, with 
“orge disk and 30 vertebrae; and Remora, distinguished from the 
second by a shorter body with only 27 vertebrae. These. re- 
markable fishes, of which about 10 species are distinguished, are 
distributed all over the tropical and warm seas, and exceptionally 
carried as far north as the south coast of England. They feed 
on other fishes, and attach themselves by means of their cephalic 
1 For the theories on the formation of the disk, cf. R. Storms, dnn. Mag. Nat. 
Hist. (6), ii. 1888, p. 67. 
