88 Morris and Buff: 



to agree more closely with the characters of the genus Asym- 

 metron than with those of the genus Branchiostoma, so a new 

 classification was formed by W. M. Tattersall, B.Sc, in his 

 paper in the Trans. Liverpool Biol. Soc, vol. xvii., where he 

 places the species in the genus Asymmetron. He divides up the 

 genus as follows : — 



A. — Species in which a urostyloid process is absent ; oral 

 cirri are present, and bear sense papillae ; ventral fin is divided 

 up into fin chambers ; single post-atrioporal caecum, 

 (i) Ventral fin possesses both chambers and rays. 



A. hassanum. 



A. hectori. 



A. inaldivense. 



A. cingalense. 

 (ii.) Ventral fin has fin chambers, but no rays. 



A. cultellum. 

 B. — Species with a long urostyloid process, into which the 

 notochord is prolonged ; oral cirri have no sense papillae ; 

 post-atrioporal caecum jDaired ; ventral fin has neither fin rays 

 nor chambers. 



A. Jucayanuvi. 



A. caudatum. 

 From the description of the species we see there is a paired 

 post-atrioporal caecum present, so we need to alter Tattersall's 

 classification slightly, and arrange group A as follows: — 



Genus Asyvimetro?i. 



A. — Species in which a urostyloid process is absent ; oral 

 cirri are present, and bear sense papillae ; ventral fin is divided 

 up into fin chambers. 



(i.) A single post-atrioporal caecum. 



(a) Ventral fin possesses both chambers and rays. 



A. hector i. 

 A. maldivense. 

 A. riur/alense. 



(b) Ventral fin has chambers but no rays. 



A. cuUelhim. 

 (ii.) k paired post-atrioporal caecum. 

 A. hassanum. 



