A HISTORY OF ESSEX 



(Jurine), and M. hirsuticornis, Norman and Brady, of which Mr. Scour- 

 field writes : ' Without doubt this is one of the best records in the 

 whole list of Epping Forest Entomostraca. Since the species was first 

 described in 1867, it appears to have been only once again recorded 

 in the British Isles, 1 and on the continent it has only been found by 

 a few observers. It is a fine species, being in fact the largest of the 

 genus. Numerous specimens were taken in Connaught Water on 

 March 10, 1894, but curiously enough none could be found about 

 a month later, nor has the species been seen again.' 



The fourth family of this section has been called by several writers 

 Lynceidse, a name which properly belongs to the phyllopod family 

 Limnetidae, and which cannot in any case be used for a group in which 

 there is now no such genus as Lynceus. The present family must be 

 called Chydoridas, from its earliest genus Chydorus, instituted in 1 8 1 6 

 by W. E. Leach, who may be regarded as the founder of English 

 carcinology. To Essex are assigned Chydorus sphcericus (O. F. Miiller),one 

 of the excessively common species ; C. ccelatus, Schodler ; C. latus, Sars ; 

 C. globosus, Baird. From the numerous other genera Mr. Scourfield 

 records Eurycercus lamellatus (O. F. Miiller) ; Acroperus harpa, Baird, 

 with a large variety perhaps equivalent to Koch's Lynceus leucocephalus ; 

 Camptocercus rectirostris, Schodler, which is perhaps Baird's C. macrourus ; 

 Leydigia quadrangularis (Leydig), with a name of rather doubtful validity ; 

 Graptoleberis testudinaria (Fischer) ; Alona guttata, Sars ; A. tenuicaudis, 

 Sars ; A. quadrangular is (O. F. Miiller) ; A. ajpnis, Leydig ; A. costata, 

 Sars ; A. rectangula, Sars, to take the place of A. intermedia, Sars, an earlier 

 record now cancelled ; A. rustica, T. Scott, ' only obtained by washing 

 pieces of wet moss'; Alonella excisa (Fischer) ; A. nana (Baird), smallest 

 of known arthropods ; A. rostrata (Koch) ; Pleuroxus trigonellus (O. F. 

 Miiller) ; P. uncinatus, Baird ; Peracantha truncata (O. F. Miiller) ; and 

 Monospilus tenuirostris (Fischer). Of the last Mr. Scourfield says : 'The 

 presence of this very peculiar species in the forest district was first 

 ascertained by its being found in the stomach of a roach from the Eagle 

 Pond. It has since been taken with the net from the same piece of 

 water.' The genus Monospilus, Sars, has more than one character that 

 may well claim to arrest the student's attention. Thus M. Jules Richard 

 observes, ' Exuviation is the rule among Cladocera, but in some cases the 

 old carapace is not shed ; it remains on the new one, so that we have 

 the appearance of lines of growth fringed with setae as in Ilyocryptus and 

 Monospilus? 2 This, it will be remembered, is a regular and prominent 

 feature in the bivalved phyllopods. Another character is enjoyed by 

 Monospilus uniquely among the Cladocera, and to this it is indebted for 

 its rather singular name, meaning ' with only a spot.' The rest of the 

 Cladocera have each a single median eye, composed of more or less 

 numerous elements, and in addition to this they sometimes have, and 

 sometimes have not, on the ventral face of the head a small mass of 



1 Scott and Duthie, Fishery Board for Scotland, \\th Ann. Rep. p. 229 (1896). 

 * Annales des Science Naturelles, ser. 7, vol. xviii. p. 309 (1895). 



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