tion, that the tail was furnished with two long setae, with a flap 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 refeiTed 

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

 The three species which have been described are — 



1. Leptdurus productus, Bosc. Clypeo corporis magis quam 

 ires partes tegente, ovato, elongato, olivaceo-viridi ; setts caudcB 

 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 ; detectain Gallia, Suecia, Borussa, &c. Museum 

 Britannicum. 



This species is of an olive-green hue, and is smaller than the Apus 

 cancriformis. The carapace is of an oval form and covers more 

 than two-thirds of the body. The notch at its posterior part is less 

 deeply lunated than in Apus cancriformis, and the keel which runs 

 down its centre is well-marked. The flap of the caudal segment is 

 of an elongated oval shape and has a keel running down its centre, 

 which, as well as its edges, are finely serrated, or beset with nume- 

 rous short setae. The tail-setae are also furnished on each side with 

 numerous short hairs, which, when magnified, present a fine plu- 

 mose appearance. The first pair of feet or rami are very small, aud 

 when the animal lies prone are indistinctly visible. 



2. Lepidurus glacialis, Kroyer (Tab. XXIL fig. 2). Clypeo 

 corporis tres partes tegente, rotundato, viridi ; setis caudce plu- 

 mosis ; lamina caudali abbreviata, sub<piadrata, denticulata. 



Long, toti corporis 1 poll. ; lat. clypei '5 poll. 



Apus glacialis, Kroyer, Voy. en Scandinavie, Lappouie, &c. t. 40. 

 f. 1. 



Hab. Li America boreali ; detecta ad " Cape Krusenstern " mense 

 August! 1849. CoUegit Dominus J. Rae. Museum Britannicum. 



This species is smaller than the preceding, and of a green colour, 

 having the carapace of a rounded form with a sharp keel running 

 down the centre. It covers rather more than two-thirds of the body, 

 and has the notch at its posterior extremity small and finely toothed 

 on its edges. The spines on the body are small and of the same 

 colour as the body itself. The first pair of feet or rami are very 

 short, scarcely visible when the animal is in a prone position beyond 

 the edge of the carapace. The tail-setae are finely plumose, and the 

 flap between them is of a somewhat square shape, short and toothed 

 on its edges. 



3. Lepidurus viridis, Baird. Clypeo corporis magis quam di- 

 midiam partem tegente, rotundato-ovali, viridi, valide carinata ; 



