322 History of British Entomostraca. 



Roesel, der Insecten Belustigung, Tom. iii. p. GOG, tab. 98, fig. 1, % 4, 1755. • 



Monoculus quadricornis, Linne, Fauna Succica, No. 2049, 1746. 



Baker, Microscope made easy, p. 98, plate 9, fig. 1, 2, 1743. Figures co- 

 pied from Philos. Transact. 



Philosophical Transactions, No. 288, accompanying plate, fig. 5, 1703 



Figure tolerably correct. 



Leeuwenhoek, Epistola? ad Societatem regiam anglicam, p. 142, fig. 1, 2, 3, 

 1699 — Figure incorrect. 



Blancardus (Stephanus) Schou-burg der Rupsen, Wormen, ma'den, &c. 

 p. 151, tab. 13, fig. B. 1688 — A very bad figure. 



Habitat. — Standing water, every where, all the year round. 



Description. — From 7-12ths to 9-12ths of a line long Body 



(Plate VIII. Fig. 1. a,) of four segments. Tail (6) of six — the latter 

 terminating in two lobes. First ring of body much larger than any 

 of the others, being equal in size to the other three. Second and 

 third nearly equal in size, the fourth being smallest. Antennae 

 (c, c,) of numerous articulations, from seventeen to twenty ; each ar- 

 ticulation throws forward a seta, sometimes two. In male, both 

 antennae (Fig. 2, a, a,) possess a peculiar swelling and hinge-joint. 

 Antennules (Fig. 1, d. d.) of four articulations, each furnished with 

 several setae, terminating one having six, of unequal length. Inter- 

 nal mandibles (Fig. 4,) composed of three parts, body («,) neck (6,) 

 and " barbillon" (c.) Body of an ovoid shape, convex on upper 

 and concave on under surface, in which concavity is lodged its 

 motor muscle. Neck, a sort of petiole turned upon itself, and di- 

 lated at extremity, in which are implanted six pretty strong teeth. 

 " Barbillon," composed of one ring and two long filaments. Exter- 

 nal mandibles (Fig. 5,) situate a little behind the others, convex ex- 

 ternally and concave internally, give origin to several filaments and 

 processes, and are terminated by two strong horny teeth. This or- 

 gan does not exist in the other species. Hands ; (Fig. 6,) each is 

 divided to the base into two parts ; the internal (a,) which Jurine 

 compares to a thumb, is much smaller than the other, is formed of 

 three articulations, the two first of which have on inner edge seve- 

 ral pretty strong plumose spines or setse, while the third, which is 

 much the smallest, is terminated by three spines. External divi- 

 sion (b,) is also composed of three articulations, upon the first of 

 which reposes the thumb ; the second is much longer, and has on 



* The figure of the Cyclops is given in this plate by Roesel, chiefly as being 

 the resting-place for a species of polype which he describes, and with which, as 

 often happens, the body of the insect is almost completely covered. Though 

 not very correct, it is much superior to the figures given by Eichhorn, Baker, 

 Geoffroy, &c and really forms with its clusters of polypes a very pretty plate. 



