A REVISION OP THE BRANGHIOSTOMID^. 3J3 



3. Amphioxus caribseus, PI. 34, fig. 5. 



Branchiostoma cabib^um, Sundevall. ' Ofvers. vet. Akad. Forsk.,' 



vol. X, 1853, p. 12. 



Myotomes, maximum number 61, minimum number 59, 

 most usual number 60 (in eight specimens, J. W. K.). Myo- 

 tome formula 37, 15, 9; 38, 14, 7; 37, 15, 8 (most usual). 



Dorsal fin low — one eighth of the height from the crest of 

 the fin to the free edge of the metapleur at mid-region of body. 

 Fin-ray chambers commence in front of the eye-spot, and 

 extend to myotome 55. Rostral fin marked off from the 

 dorsal fin by a shallow notch, and terminating bluntly in 

 front. Caudal fin small and shallow. Ventral fin low, with 

 fin-ray chambers and paired fin-rays. Oral sphincter underlies 

 the apex of myotome 5, and is provided with twelve intra- 

 buccal cirrhi. Prseoral tentacles and gonad pouches as in A. 

 lanceolatus. 



Maximum length among eight specimens 4 cm. (J. W. K.) ; 

 according to Sundevall 5*1 cm. 



Distribution. — East coast of the United States and of 

 South America; West Indies. 



Remarks. — This species stands very near to A. lanceo- 

 latus. It is distinguished from that form chiefly by the 

 slight development of the caudal fin and the shortness of the 

 post-anal region. 



4. Amphioxus Belcheri, PI. 35, fig. 8. 



Beanchiostoma Belcheri, Gray. 'Proc. Zool. Soc.,' 1847, p. 35. 



Myotomes, maximum number 65, minimum number 63 (in 

 four specimens examined in the British Museum (J. W. K.). 

 Myotome formula 37, 14, 14 = 65 (according to Giinther) ; 

 38, 17, 10 = 65 (J. W. K.) ; 37, 16, 10 = 63 (J. W. K.). 



Rostral fin well marked, and separated from the dorsal fin by 

 a depression. Notochord dipping downward before its anterior 

 termination. Inferior lobe of the caudal fin relatively large. 



