294 Part III. — Ninth Annual Report 



The sculpture of this exceedingly small species is like that of no other 

 Lynceii. It consists of bold and obliquely curved striae, and not merely 

 impressed lines, which impart a beautifully fluted appearance to the shell 

 when the light strikes across the striee. My specimens differ somewhat 

 from that figured by Norman and. Brady in the work cited, in the rostrum 

 being less curved — being in fact nearly straight — whereas the figure shows 

 the rostrum curving inwards considerably. My specimens agree better 

 with the figure of A. pygmcea in Herrick's report. It seems to be a some- 

 what rare species. 



Peracantha, Baird. 



Peracantha truncata (Muller). 



1781. Lynceus truncatus, Muller, Entomostraca, p. 75, pi. ii. figs. 4-6. 

 1850. Peracantha truncata, Baird, Brit. Entom., p. 136, pi. xvi. fig. 1. 

 1867. Lynceus truncatus, Nor. and Brady, loc. cit., p. 387, pi. xxi. fig. 9. 

 1884. Pleuroxus truncata, Herrick, loc. cit., p. 112. 



This is one of the more distinctly characterised species, the posterior 

 extremity of the carapace is subtruncate and "armed all along the edge 

 with a series of large tooth-like processes, the hindermost of which are 

 directed backwards; surface of shell divergently striated." I have followed 

 Norman in retaining Baird's generic name, Peracantha.* 



Pleuroxus, Baird. 



Pleuroxus Icevis, G. 0. Sars. 



1844. Lynceus trigonellus, Zaddach, Syn. Crust. Pruss. Prod., p. 28. 



1861. Pleuroxus Icevis, G. 0. Sars, Om. de i Orneg. af Christi., forekom. Clad., 



p. 22. 

 1867. Lynceus Icevis, Nor. and Brady, loc. cit., p. 389, pi. xviii. fig. 5 ; pi. xxi. 



fig. 14. 

 1884. Pleuroxus hastatus, Herrick, loc. cit, p. 108, pi. i. fig. xvi. 



This species may be distinguished from the others by the form of the 

 post-abdomen, which narrows gradually towards the claws. The claws 

 are furnished with two basal spines. With a low power of the microscope 

 the carapace appears faintly costate, but under a moderately high power 

 (J inch) the surface is seen to be reticulate, besides being finely striate 

 longitudinally. 



Pleuroxus trigonellus (Muller). 



1776. Lynceus trigonellus, Muller, Zool. Dan. Prod. No. 2395. 



1850. Pleuroxus trigonellus, Baird, Brit. Entom., p. 134, pi. xvii. fig. 3 (fern.). 



1850. Pleuroxus hamatus, idem ibidem, p. 136, pi. xvii. fig. 5 (mas.). 



1867. Lynceus trigonellus, Nor. and Brady, loc. cit., p. 391, pi. xxi. fig. 11. 



1884. Pleuroxus trigonellus, Herrick, loc. cit., p. 108. 



A widely distributed species, but seldom very abundant. The post- 

 abdominal claws are furnished with one basal spine. 



Pleuroxus uncinatus, Baird. 



1850. Pleuroxus uncinatus, Baird, Brit. Entom., p. 135, pi. xvii. fig. 



1867. Lynceus uncinatus, Nor. and Brady, loc. cit., p. 393, pi. xviii. fig. 9 ; pi. 



xxi. fig. 13. 

 1884. Pleuroxus uncinatus, Herrick, loc. cit., p. 114. 



This seems to be widely distributed though not very common. It varies 

 a good deal in the shell sculpture. There are also slight modifications in 

 the form of the carapace ; the greater number of our specimens have the 

 nostrum more closely appressed to the shell than in those figured by 

 Norman and Brady, and in this respect they agree more closely with 

 Baird's figure. The post-abdomen is similar to Norman and Brady's 

 figure. 



* See Museum Normanianum, pt. iii. (1886). 



