A REVISION OF THE BRANCHIOSTOMID^. 311 



Gustatory groove of Hatschek (on the right side of the 

 roof of the prseoral hood) shallow. 



Sub-genus 1. — Amphioxus. 



Amphioxus, Yarrell. 



Both metapleura terminate immediately behind the atriopore, 

 and overlap the median ventral fin. The ventral fin-ray 

 chambers form a single median series, each containing a pair 

 of fin-rays, excepting the more anterior and more posterior 

 chambers. 



Gonad pouches developed on both right and left epipleura. 



1. Amphioxus lanceolatus, PI. 34, fig. 1. 



LiMAX LANCEOLATUS, Pallas. ' Specil. Zool.,' X, p. 19. 

 Beanchiostoma lubricum, Costa. 'Cenni Zool.,' Napoli, 1834, 



p. 49. 

 „ „ „ * Frammenti Anatomia Compa- 



rata,' fas. i, Napoli, 1843. 

 Amphioxus lanceolatus, Yarrell. 'British Fishes,' 1836, p. 462. 

 Bbanchiostoma lanceolatum, Gray. 'Cat. Brit. Mus. Fish.,' 



vol. vii, p. 150, 1851. 



Myotomes, maximum number 63, minimum number 58, 

 most frequent 60 (J. W. K. 50 specimens) ; myotome formula 

 (prseatrioporal, prseanal, post-anal) 36, 15, 10 (cf. Lankester) ; 

 35, 14, 12 (cf. Andrews); 35, 14, 11 (J. W. K.). 



Dorsal fin of moderate height, namely, one seventh of the 

 height from the crest of the fin to the free edge of the metapleur 

 at the mid-point of the animal's length. 



Snout or rostral fin small and pointed, not marked off from 

 the dorsal fin. Caudal expansion of the dorsal and ventral fin 

 long and lancet-shaped with sharp angles. 



Ventral fin with a variable number of median fin-ray 

 chambers, in each of which are two paired fin-rays (excepting 

 those at either end of the series). Thirty-four to forty-one 

 pairs of ventral fin-rays present. 



Oral sphincter placed in a line drawn vertically from the 

 apex of the anterior angle of the seventh myotome. 



