220 ARTHUR WILLEY. 
and swims with exactly the same motions of the body as 
Amphioxus, which is not the case with most other Annelids, 
At first I thought I was obtaining a fine series of Amphioxus, 
but the great majority turned out to be Ophelids. 
The species now to be described, for which I propose the 
name Asymmetron caudatum, n. sp., adopting Kirkaldy’s 
system! of subdivision of the Branchiostomide, is perhaps 
interesting on account of its geographical distribution relative 
to other species of Amphioxus, rather than from the possession 
of novel features. 
That it should be entirely distinct from its relatives in 
Torres Straits, from whom it is removed by a distance of less 
than six hundred miles, and, on the other hand, closely allied 
to a species residing in the Bahamas, upwards of eight thousand 
miles away, on the other side of the American continent, is 
certainly a noteworthy fact in distribution. 
The specific differences between species of Amphioxus are 
frequently of apparently little moment, but may be of im- 
portance when taken in conjunction with geographical distri- 
bution. On this principle the Japanese Amphioxus recently 
described by Andrews?” should at least be regarded as a marked 
variety of rather than identical with Amphioxus Belcheri. 
As mentioned above, I only succeeded in obtaining two 
individuals of Asymmetron caudatum, because the unpro- 
pitious season of the year, when one is liable to be overtaken 
by westerly gales, rendered it imadvisable to delay for any 
considerable length of time in the lagoon. 
The larger specimen was an immature female, and measured 
29°5 mm.; the other was a mature or submature male, 
measuring 20 mm. in length. Other differences, particularly in 
respect of the caudal fin (cf. figs. 1 and 3), occurred between 
the two individuals ; and these differences, combined with the 
marked contrast in size, would seem to point to a sexual 
1 Kirkarpy, J. W., * A Revision of the Genera and Species of the Branchio- 
stomide,” ‘ Quart. Journ. Mic. Sci.,’ vol. xxxvii, 1895, pp. 8303—323. 
2 AnpRews, HE. A., “An Amphioxus from Japan,” ‘ Zool. Anz.,’ 1895. 
This should be named A. Belcheri, var. japonicus. 
