458 ' The American Naturalist. ‘[May, 
apparently represented by the B. pelagicum of Giinther, which 
may be named Amphiozides. The principal distinctive charac- 
ters of generic importance appear to be the development of the 
gonads in two lateral rows or their restriction to one (right) 
side, the extent of the metapleural folds, the presence or want 
of what is generally called the ventral fin (sympodium), the 
-extent and structure of the dorsal fin,’ and the form of the pos- 
terior end of the body or tail. 
The genera may be briefly defined as follows: 
BRANCHIOSTOMA. 
Branchiostomids with bilateral gonads, a rayed sympodium, 
low dorsal fin, and sagittiform expansion of caudal fin mem- 
branes. 
Contains B. lanceolatum and most other species. 
PARAMPHIOXUS. 
Branchiostomids with unilateral gonads, a rayed sympodium, 
low dorsal fin, and expanded caudal membranes. 
EPIGONICHTHYS. 
Branchiostomids with unilateral gonads, a reduced rayed 
sympodium, elevated:dorsal fin, and expanded caudal fin- 
membranes. | 
ASYMMETRON. 
Branchiostomids with unilateral gonads, no sympodium, low 
dorsal fin, and an extended attenuated tail. 
AMPHIOXIDEs, 
Branchiostomids with bilateral (?) gonads, no rayed sym- 
podium (?), low dorsal fin, expanded caudal membranes, and 
oral cirri aborted (??). 
| The so-called rays (Actinomimes) and their inclosing chambers (actinodomes) 
are characteristic of the Branchiostomids. 
26 
