HETEEOPLRURON HECTOBT, NEW ZEALAND LANCELET. 279 



with a length of 43 mm. ; in total number of myotomes, too, 

 it exceeds any Amphioxid hitherto described — the nearest 

 approach being seventy-nine in "A. elongatum" of San- 

 deval, and seventy-eight in H. bassanum. 



It is pei'haps worth noting that this excess is chiefly due 

 to an increase in tlie number of pre-atrioporal segments; for 

 the post-anal segments in other species are from eiyht in H. 

 cingalense to fourteen or even seventeen in H. bassanum, 

 with an interporal number of ten to seventeen in the 

 various species. 



In regard to the caudal fin, there is equally sufficient evi- 

 dence of distinctness, for whereas in H. bassanum it com- 

 mences behind the anus, in H. cingalense it arises 

 immediately in front of it, and is very short ; while in H. 

 cultellum, though it begins at a point further forward, yet 

 this point is some distance relatively behind its point of 

 origin in H. hector i, while the position of the greatest 

 depth is behind the anus in all three, instead of being ante- 

 rior to ii., as in the present species. 



The sea surrounding Australia and the neighbouring* 

 islands is evidently rich in species of Branchiostomidte, for 

 already four species belonging to each of the three known 

 genera have been recorded, — viz. Amphioxus belcheri. 

 Gray, from Toi-res Straits, as well as from the const of 

 Borneo; Heteropleuron cultellum, Peters, from Torres 

 Sti-aits and further east coast of Australia; Asymmetrou 

 can datum, Willey, from the Louisiade Archipelago,^ due 

 east of the Torres Straits; a~ud H. bassanum, Giinther, 

 froTii the south of Australia, from Bass's Straits. The 

 present species thus makes the fifth in these southein seas; 

 its habitat is two thousand miles or more distant from each 

 of these localities. These seas appear to be the home of 

 the asymmetrical species, and one is tempted to think that 

 these may be the more primitive of the family, especially as 

 my species presents one, perhaps two survivals apparently 

 of a larval condition. 



' 'Quart. Joiirii. .Mirr. Sci.,' vol. xxxix, p. 210. 



