426 MARGARET ROBINSON. 



Since writing the above I have read a paper in the 

 ' Quarterly Journal of Microscopical Science,' for December, 

 1905, in which the author, G. H. Carpenter, while suggesting 

 that the Leptostraca are the most primitive Crustacea, and 

 admitting their nearness to the Malacostraca, to which he 

 says ^' they may be, to some extent, ancestral," states that he 

 considers their nearest relations among the Entomostraca to 

 be not the Phyllopods but the Copepods. This leads me to 

 think that, since it has been my aim to emphasise the Mala- 

 costracan position of Nebalia, and its nearness to the 

 Mysidge, I have, perhaps, rather implied than explicitly stated 

 (as I should have done), that though one cannot now think 

 that Nebalia is descended from the Phyllopods, or, indeed, 

 from any of the Entomostraca, yet I believe that its nearest 

 allies among the Entomostraca are the Phyllopods. It seems 

 to me that, leaving aside other points of resemblance between 

 Branchipus and Nebalia, the likeness between the thoracic 

 limbs of Nebalia and those of Branchipus and Apus 

 cannot be accounted for by homoplasy. Thinking over this, 

 I have been led again to Professor Lankester's illuminating 

 papei's (1881 — 1904), the reading of which has only 

 strengthened my previous convictions. 



It seems not improbable that Nebalia is the most ancient 

 Crustacean of Avhich we know at present. Perhaps the 

 strongest piece of evidence for this view of its position lies 

 in the fact that the adult animal has three pairs of coelomo- 

 duets. If, however, I were to speculate as to the Ancestral 

 Crustacean I should be inclined to imagine it as possessing 

 the most primitive features not of Calanus, Nebalia, and 

 Triarthrus, but of Apus and Nebalia. 



March, 1906. 



References to Liteeatuke. 



Allen, E. J.— 1893. " On the Nepbridia and Body Cavity in some Decapod 

 Crustacea," ' Quart. Journ. Micr. Sci.,' vol. 35. 



