Zoological Society. 225 



distinguished from A. Guildingii by its round-shaped carapace of a 

 horny colour covering half the body of the animal, and its external 

 branch of the first pair of feet only the length of the body, while in 

 A. Guildingii it exceeds the whole body and caudal filaments in- 

 cluded. The carina down the centre of the carapace, and the fork 

 which it takes at the anterior extremity where the division into ce- 

 phalic and thoracic portions takes place, are marked throughout 

 their length with a deep brown colour, as are also the short stout 

 spines on the abdominal portion of the body. These are straight, 

 not hooked as in some of the other species. The caudal filaments 

 are nearly the length of the body, and are covered with very nume- 

 rous, extremely short setae. The oviferous feet are present in all the 

 specimens I have examined, but none contain any ova. 



Genus Lepidurus, Leach. 



Clypeus corneo-coriaceus. Corpus molle, cylindricum. tegmentum 

 caudale lamina producta instructum. Pedum primi paris ap- 

 pendices, aut rami, brevissimi. 



In the genus Lepidurus the tail-segment of the body, which in 

 Apus is rounded, is furnished with a flap or plate of considerable 

 size extending to some distance between the long setse or filaments. 

 The first pair of ^eet, compared with those of Apus, are extremely 

 short and comparatively inconspicuous. These two characters at once 

 distinguish the genus, of which only three species have as yet been de- 

 scribed. In other respects it resembles perfectly the genus Apus. 



Schaeffer is the first author who has distinctly described any spe- 

 cies belonging to the genus Lepidurus. Linnaeus' s description of 

 the *^ Monoculus Cauda biseta'' in the first edition of the 'Fauna 

 Suecica,* will apply to either the Apus or Lepidurus. He quotes 

 Frisch's figure, and states, as I have mentioned above, that he had 

 seen a specimen in London. We might conclude from this that it 

 was the Apus cancriformis he had in view ; but in the second edition 

 of the * Fauna' (1761), he distinctly mentions, in his brief descrip- 

 tion, that the tail was furnished with two long setae, with ajlap inter- 

 posed between them. As in this edition he continues to refer to 

 Frisch's figure, and adds that of Klein, in the ' Philosophical Trans- 

 actions,' it is evident he confounded two species together ; and as the 

 Lepidurus productus (the Apus productus of authors) is perhaps the 

 more common species of the two on the Continent, it is most proba- 

 ble that he had it in view when he wrote, but erroneously referred 

 to the species figured by Frisch and Klein as identical with it. 



The three species which have been described are — 



1 . Lepidurus productus, Bosc. Clypeo corporis magis quam 

 tres partes tegente, ovato, elongato, olivaceo-viridi ; setis caudce 

 pennatis ; lamina caudali elongato-ovata, carinata, setis brevi- 

 bus numerosis obsita. 



Long, toti corporis 2^ poll. ; lat. clypei 1 poll. 



Pro Synonymis vide M. Edwards, Hist. Nat. Crust, iii. 560. 



Hab. In Europa ; detecta in Gallia, Suecia, Borussa, &c. Museum 

 Britannicum. 



Ann, &: Mag, N. Hist. Ser. 2. Fb/.xiii. 15 



