A REVISION OF THE BRANCHIOSTOMID^. 317 



the sub-genus Amphioxus. It would be almost justifiable to 

 place H. cultellum in a distinct sub-genus on account of the 

 absence of fin-rays from the ventral fin-ray chambers, the 

 great depth of the dorsal fin, the swollen anterior knob-like 

 termination of the notochord, and the considerable tract of 

 terminal notochord projecting posteriorly beyond the last 

 myotome. 



Dr. Arthur Willey (loc. cit.) was the first to draw attention 

 to the unilateral character of the gonadic pouches in H. 

 cultellum, and, in fact, to all the points here noted, excepting 

 the number of the intra-buccal cirrhi. Dr. Willey states that 

 the prseoral tentacles are devoid of the projecting sensory 

 papillae which occur in all species of Amphioxus and Hetero- 

 pleuron. I find in well-preserved specimens where the epi- 

 thelium is still present that the sensory papillae are clearly 

 developed. 



Dr. Willey was unable to find an olfactory pit in this 

 species, and I have not found one. 



Genus II. — Asymmetron. 



AsYMMETRON, Aiidiews. 'Johns Hopkins University Circulars,' June, 1893, 



vol. xii, p. 104. 



Prseoral tentacles grouped into ventrad and laterad series by 

 the presence of a vei'y high intertentacular membrane uniting 

 the tentacles of the two ventrad groups, the lateral series having 

 a low intertentacular membrane like that of the whole series 

 in Branchiostoma : a median free ventral " tentaculum impar^' 

 between the two ventrad groups of high-webbed tentacles. 



Dorsal and ventral median fins expanded some distance in 

 front of the caudal extremity, and contracted again along the 

 terminal seventh of the body, so as to leave a narrow caudal or 

 urostyloid process, and no '* caudal " fin. Myotomes not 

 developed in the urostyloid process, which is, however, traversed 

 by the notochord and nerve-cord. No fin-ray chambers or fin- 

 rays present in the ventral median fin. 



Right metapleur continued without break to join the ventral 



