364 ARTHUR WILLEY. 



from the Bahamas ; but in this case the author adds the curious 

 fact that the ventral fin space is also absent. In this respect, 

 therefore, the new species differs essentially from B. cultel- 

 lum, in which separate fin-chambers are emphatically present 

 in the ventral fin. 



In B. lanceolatum the right and left raetapleural folds 

 gradually decrease in size behind the atriopore, and, while 

 converging together, finally die out on either side of the mid- 

 ventral line below the anterior portion of the ventral fin. In 

 B. cultellnra this is not the case. Here the left metapleural 

 fold gradually dies away behind the atriopore, whilst the right 

 fold does not die out, but is continued behind the atriopore into 

 the mesial ridge, which lies below the ventral fin-chambers, 

 and represents, as mentioned above, the forward continuation 

 of the caudal fin. 



This behaviour of the right metapleur has also been pre- 

 viously signalised by Andrews in the Bahama species. 



In the latter, again, according to Andrews, the buccal cirri 

 are '' smooth and united by the hood membrane for the greater 

 part of their length." In B. cultellum, on the other hand, 

 the cirri are distinctly free throughout their entire length, 

 except, of course, at their bases, which are embedded in the 

 margin of the oral hood ; at the same time they appear to be 

 without those papilliform prominences which are a well- 

 known feature in the European species. 



I have been unable to detect an olfactory pit in B. cul- 

 tellum, but will not undertake to say that it is always absent. 

 It appears, however, according to Andrews, to be absent in the 

 Bahama species.^ 



' That this is a distinct species is shown once for all (in the absence at 

 present of the detailed illustrated description which I am informed by 

 Professor Andrews will shortly appear in vol. v of the ' Studies from the 

 Biol. Lab, Johns Hopkins University ') by the formula of the myotomes as 

 given by Andrews, viz. 44 + 9 + 13 = 66. Length 13—16 mm, 



[Since the above was in type Andrews' memoir has appeared in the 

 * Bulletins of the Biol. Lab. of the Johns Hopkins University/ vol. v, 

 No. 4, under the title " An Undescribed Acraniate : Asymmetron luca- 

 yanum." — Editor]. 



