CLASSIFICATION OF THE CEPHALOCHORDA. 301 



with, or without ventral fin chambers or 

 rays ; post-atrioporal coeca 1-2 in number. 

 (^4) 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 coecum. 

 (i.) Ventral fin possesses both chambers 

 and rays. 



A. bassanum — Length 43 mm. ; 

 myot, 70-78; formula 45, 16, 

 14 ; rostral fin well developed ; 

 31-33 oral cirri ; oral sphincter 

 over 7th myot. ; 16 intra-buccal 

 tentacles ; 26-31 gonads ; ventral 

 fin rays single. 1 

 A. hector i — Length 53 mm. ; myot. 

 84; formula 53, 19, 12; ventral 

 fin rays and chambers prolonged 

 postanally. Other characters as in 

 A. bassanum. 

 A. maldivense- — Length 22 mm. ; 

 myot. 73 ; formula 45, 16, 12 ; 

 dorsal fin swollen anteriorly ; 

 gonads 26 ; ventral fin rays 

 single; oral cirri 23. Other 

 characters as in A. bassanum. 

 A. cingalense — Length 27 mm. ; 

 myot. 61-64 ; average formula 

 39, 16, 8 ; gonads 20-26 ; ventral 

 fin rays double ; oral cirri 26-32 ; 



1 There seems considerable doubt as to whether the fin rays are 

 paired or single. Miss Kirkaldy (loc. cit.) states that they are paired. 

 Dr. Benham (loc. cit.), on the other hand, asserts they are single. 



