272 TRANSACTIONS LIVERPOOL BIOliOGICAL SOCIETY. 



exact outline, and to make their shape a generic character 

 appears to be most unsatisfactory. GKinther, in 1884, * 

 re-examined this species and found that the vent was 

 not median, but, as in all other then known species, was 

 distinctly on the left side; he therefore very rightly 

 referred the species back to the genus Branchiostoma. 

 Although, as we shall see later, Peters' form was a type 

 of a new genus, which has since been recognised, it was 

 certainly not distinct generically on Peters' characters 

 stated above. In the same paper Gunther summarises 

 the species of Branchiostomidse and adopts Sundevall's 

 method of enumerating the myotomes in the determin- 

 ation of species. Thus he now recognises as five distinct 

 species what he, in 1870, regarded as forming one. He 

 also added a new species, B. bassanum, for a Lancelet 

 from Bass Strait, Australia. His six species (1884) are 



B. elongatum - 49, 18, 12 



44, 13, 18) 

 B. bassanum - - - ■ 43, 15, 17 - 



, 45, 14, 17,1 

 B. belcheri - 37, 14, 13 



B. caribbaum - - - 37, 14, 9 



(34,13,13) 

 B. lanceolatum - - - 1 35, 12, 12 - 



( 36, 14, 111 



B.cultcllum- - - - 32,10,10 



This summary was, however, not quite complete, as 

 it did not include H. californiense, a species formed by 

 J. G. Cooper in 1808, 2 for a form found in San Diego Bay, 

 California. Finally, Gunther 3 added a new species in 



i Report, Zool. Collect, TI.M.S. "Alert." 1884. 

 aNat. Wealth CaJifor., Cronis'e. 1868. 

 b Challenger Keports. Vol. xxxi. 1889. 



