of the Fishery Board for Scotland. 293 



Lynceus quadrangularis, Miiller. 



1776. Lynceus quadrangularis, Miiller, Zool. Dan. Prod., p. 199, No. 2393. 

 1850. Alona quadrangularis, Baird, Brit. Entom., p. 131, pi. xvi. fig. 4. 

 1860. Lynceus affinis, Leydig, Naturges. der Dapli, p. 223, pi. xi. figs. 68, 69. 

 1867. Lynceus quadrangularis, Nor. and Brady, loc. cit., p. 377, pi. xxi. fig. 5. 

 1884. Alona quadrangularis, Herrick, loc. cit, p. 97, pi. E, figs. 1, 2. 



A widely distributed and common species, with which Alonopsis elongatus 

 has probably been included, though this latter species is easily distinguished 

 by its greater size and by the form of the post-abdomen, and the armature 

 of the terminal claws of the same. 



Lynceus costatus (G. 0. Sars). 



1862. Alona costata, G. 0. Sars, op. cit., Audet Bidrag., p. 38. 



1867. Lynceus costatus, Nor. and Brady, loc. cit., p. 379, pi. xviii. fig. 2 ; pi. 



xxi. fig. 7. 

 1884. Alona costata, Herrick, loc. cit., p. 97. 



This species is considered by Herrick as a not very satisfactory one, 

 being " founded practically upon the absence of the eighth seta of the 

 antennae." The post-abdomen is short, moderately broad, and of nearly 

 equal breadth as far as the superior marginal spines extend, and the 

 termination of the superior margin is produced to form a distinct angle. 



Lynceus guttatus (G. 0. Sars). 



1862. Alona guttata, G. 0. Sars, op. cit., Andet Bidrag., p. 38. 



1867. Lynceus guttatus, Nor. and Brady, loc. cit., p. 380, pi. xviii. fig. 6 ; 



pi. xxi. fig. 10. 

 1884. Alona guttata, Herrick, loc. cit., p. 94. 



This comes near to the last, but the post-abdomen is shorter and more 

 hollowed out on the superior margin immediately in front of the marginal 

 spines. The surface of the carapace is frequently ornamented by cellular or 

 pit-like impressions it is also rather smaller than L. costatus. 



Alonella, Sars. 

 Alonella exigua (Lilljeborg). 



1853. Lynceus exiguus, Lillj., De Crust, in Scania Occnrr. , p. 79, pi. vii. figs. 9, 



10. 



1854. Lynceus excisus, Fischer, Bull, de Soc. Imp. des Nat. de Moscou, p. 428, 



pi. iii. figs. 11-14. 

 1862. Alonella excisa, G. 0. Sars, op. cit, Andet Bidrag., p. 52. 

 1867. Lynceus exiguus, Nor. and Brady, loc. cit., p. 384, pi. xviii. fig. 3; pi. xxi. 



fig. 3. 

 1884. Alonella excisa aud exigua, Herrick, loc. cit, pp. 103-105, pi. E, fig. 6 ; 



pi. G, figs. 10, 11. 



The two forms here referred to are by some authors considered as 

 distinct species, but so far as I can make out from the descriptions and 

 figures of the authors cited, the chief difference between A. exigua and 

 A. excisa is, that in the first, the carapace is smooth or nearly so, whereas 

 in the second it is distinctly reticulated and marked between the reticula- 

 tions by distinct and close-set striae. This difference does not seem to be 

 of sufficient importance to be specific. The post-abdomen, so far as I can 

 make out from the specimens examined, is similar in form in both, the 

 antennae also of both are similar. I have therefore included both in 

 Lillj eborg's species. 



Alonella nana (Baird). PI. ii. fig. 6. 



1850. Acroperus nanus, Baird, Brit. Entom., p. 130, pi. xvi. fig. 6. 



1860. Lynceus nanus, Leydig, Naturges. der. Daphn. , p. 228. 



1862. Alonella pygmcea, G. O. Sars, op. cit, Andet Bidrag., p. 48. 



1867. Lynceus nanus, Nor. and Brady, loc. cit., p. 396, pi. xviii. fig. 8 ; pi. xxi. 



fig. 8. 

 1884. Alonella pygmoea, Herrick, loc. cit., p. 105, pi. H, fig. 7. 



