of the Fishery Board for Scotland. 295 



Chydorus, Baird. 



Chydorus globosus, Baird. 



1850. Chydorus globosus, Baird, Brit. Entom., p. 127, pi. xvi. fig. 7. 

 1867. Lynceus globosus, Nor. and Brady, loc. cit., p. 398, pi. xx. fig. 5. 

 1884. diydoruslglobosus, Herrick, loc. cit., p. 116, pi. F, figs. 1, 2, 3, and 9. 



This fine species does not appear to be very common in Scotland. It 

 was obtained by Mr D. Robertson, F.L.S., many years ago in the Paisley 

 Canal (where I also found it later on), and in the Hebrides by Rev. A. 

 M. Norman. It is recorded from several places both in England and 

 Ireland. 



Chydorus sphcericus (Miiller). 



1776. Lynceus sphcericus, Miiller, Zool. Dan. Prod., No. 2392. 



1850. Chydorus sphcericus, Baird, Brit. Entom., p. 126, pi. xvi. fig. 8. 



1884. Chydorus sphcericus, Herrick, loc. cit., p. 116, pi. F. figs. 4, 7, 8, 10. 



Chydorus sphcericus is one of the commonest species of the Lynceidse. 



Monospilus, G. O. Sars. 



Monospilus tenuirostris (Fischer). PI. i. fig. 1. 



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



427, pi. M, figs. 7-10. 

 1861. Monospilus dispar, G. 0. Sars, op. cit., p. 23. 

 1867. Monospilus tenuirostris, Nor. and Brady, loc. cit., p. 403, pi. xix. fig. 2 ; 



pi. xx. fig. 9. 

 1884. Monospilus dispar, Herrick, loc. cit., p. 119, pi. i. fig. 21. 



This Lynceid differs from all the other species in having only the larval 

 eye present during all stages of growth, and in the ecdysis not being com- 

 plete, so that the old shell, instead of being cast off, remains attached to 

 the new one, which projects more or less beyond the old. The result is 

 that there are in adult specimens the appearance of more or less regular 

 growth lines, similar to that observed in some Lamellibranch molluscan 

 shells. The head is articulated to the carapace so slightly as to easily 

 become detached from it Herrick speaks of it as the " rarest of all 

 Entomostraca." He regards it "as a degraded offshoot of the more typical 

 stem of the Lynceidse." 



PoLTPHEMIDuE. 



Polyphemus, Miiller. 



Polyphymus pediculus (Linne). 



1746. Monoculus pediculus, Linne, Faun. Suec, No. 2048. 



1776. Polyphemus occulus, Miiller, Zool. Dan. Prod., No. 2417. 



1850. Polyphemus pediculus, Baird, Brit. Entom., p. Ill, pi. xvii. fig. 1. 



1884. Polyphemus pediculus, Herrick, loc. cit., p. 121, pi. B, figs. 4-6. 



This is a moderately common species, especially in large sheets of water. 



Bythotrephes, Leydig. 



Bythotrephes longimanus, Leydig. 

 Bythotrephes longimanus, Leydig. 

 Bythotrephes cederstromii, Schcedler. 



Bythotrephes often occurs in considerable abundance ; it is easily dis- 

 tinguished by its having an abdominal spine of enormous length. 



