CRUSTACEOLOGY. 



S8<> 



Cjustacca. 



Longicor- 

 bis. 



10. POIY- 

 1'HEMUS, 



Oculus. 



11. ZOE. 



Telagica. 



1?. Br,vx. 



( IIIUI'OOA. 



sisgnalis. 



Sp. 2. Longkornis. Two very long antennae ; tail 

 bifid. 



Monoculus longicomis, Fabricius. 



Cyclops longicomis, Miiller, Latreille. 



Inhabits the Norwegian Sea. 



Observation. The above species are very distinct and 

 ■well marked ; but we are sorry to inform our readers that 

 this is not the case with the others, all of which inhabit 

 fresh waters, but are by no means distinctly defined. 

 The species alluded to are Cyclops rubens, ccendeus, cla- 

 vigrr, and mulleri. On the latter, a long and elaborate 

 paper is given in the Annates du Museum d'Histoire 

 Naturelle for 1806, but we have heard from good au- 

 thority, that it has been described under another name 

 in the works of Miiller. We shall therefore be. silent 

 on the subject, and pass it without further notice. 



Family VI. Cep-halota. 



* Eyes sessile. 



Gexus X. PoLvriiEMUs. Head distinct from the 

 thorax. One eye. Thorax distinct from the abdomen, 

 which is oval and crustaceous, compressed and crook- 

 ed. Tail very much inflected. Two bifurcate processes 

 extended horizontally. Eight short retuse feet, armed 

 with seta;. 



Species 1. Oculus. Body greenish-grey, oars black- 

 ish. 



Inhabits marshes and lakes. Besides this, Mr Leach 

 believes there are many other species which have been 

 confounded with it : It is Polyphemus oculus of Miiller 

 and Latreille, Moiocuhis pcdicidus of Fabricius, Ce- 

 phaloadus stagnorinn of Lamarck. 



Genus XI. Zbn. Flead indistinct, with two large 

 globose eyes. Rostrum nearly perpendicular, rather 

 larger than the thorax, with the apex acute. Four an- 

 tennae inserted beneath the eyes ; the interior simple, 

 the exterior geniculated and bifid. Thorax somewhat 

 oval. Back produced into a recurved spine twice as 

 long as the thorax. Feet short, and hid under the tho- 

 rax, with the exception of the hindermost pair, which 

 are long, and formed for swimming. Tail, length of 

 the thorax, and often inflected or bent up under it, 

 composed of four joints ; the first four very narrow, 

 the last largest and lunated. 



Species 1. Pclagica. Colour cinereoxis. 



Inhabits the sea every where. 



Z'oe pelagica, Bosc, Hist. Nat. des Crust, torn. ii. p. 

 135. Monoculus taunts of Slabber. 



** Eyes with a distinct peduncle. 



Gexus XII. Branchiopob a. Body filiform, and ve- 

 ry soft. Head divided from tiie thorax by a very nar- 

 row but distinct neck. Two lateral moveable eyes. 

 Two short, double-jointed, capillary antennse, inserted 

 behind and above the eyes. Front armed with two 

 moveable tentaeulse or horns, (broader towards the apex 

 in the male,) which are notched : those of the female 

 jointed, and bearing a papilla on their point. In the 

 front of the male, at the base of the te.itaeul*, are two 

 long hair-like filaments; the clypeus in this sex is 

 double. In both sexes, the mouth has a hooked ros- 

 triform papilla, supported by four little processes. The 

 trunk of the body keel-shaped, consisting of eleven 

 joints, each bearing two branchial leet; the anterior 

 pair with two, the posterior with three lamellae. The 

 t,:il about the length of the body, composed of six? or 

 nine? obscure joints; the anal segment bearing two 

 fins. The organs of generation situated at the base of 

 the tail. 



Species 1. Slagncdis. Body transparent, of a Bght- 



brown colour, slightly tinged with green o\ blue, par- Crustacea, 

 ticularly on the head and legs. *■■ ""Y"" - ' 



Cancel- stagnulis of Linne and Shaw, Gammarus stag*- 

 na/is of Fabricius, Branchiopoda stagnalis of Lamarck 

 and Latreille, Apus pieiformis of SchaeiTer. 



A most ingenious and accurate paper has been writ- 

 ten on this species by Dr George Shaw, in the Trans- 

 actions of the Lhmean Society of London, vol. i. of 

 winch we shall here avail ourselves. 



" It is generally found in such waters as are of a 

 soft nature, and particularly in those shallows of rain- 

 water which are so frequently seen in the spring and au- 

 tumn, and in which the Monoculus pulex of Linne, and 

 other small animals, abound. At first sight, it bears 

 some resemblance to the larva of a dytiscus ; but when 

 viewed closely it is found to be of a much more curious 

 and elegant appearance than that animal. The legs, of 

 which there are several pair (eleven?) on each side, 

 are flat and filmy, and have the appearance of so many 

 waving fins, of the most delicate structure imaginable. 

 The whole animal is extremely transparent, and the 

 general colour is brown, slightly tinged with bluish- 

 green. These creatures should seem, by their appear' 

 ance, to be of a predaceous nature, the structure of 

 their fangs seeming to be particularly adapted to the 

 purpose of seizing their prey ; yet (Dr Shaw observes) 

 I never observed those which I kept to attack any of 

 the animalcules which were in the same water ; on the 

 contrary, Monoculus conchaceus of Linne very frequent- 

 ly assaults them, and adhei-es with such force to their 

 tails or legs, as sometimes to tear off a part in the 

 struggle. It delights mixch in sunshine, during 

 which it appears near the surface of the water, swim- 

 ming on its back, and moving in various directions, by 

 the successive undulations of its numerous fin-like legs, . 

 and moving its tail in the manner of a rudder. On the 

 least disturbance, it starts in the manner of a small fish, 

 and endeavours to secrete itself, by diving into the soft 

 mud. It changes its skin at certain periods, as is evi- 

 dent, from the exuviie or slough being frequently found 

 in the water in which these animals are kept. 



Linne, as appears in the last edition of the Fauna 

 Succica, had observed this animal, but, though he par- 

 ticularly mentions the appearance of the ovarium, he • 

 proposes a most extraordinary doubt, whether it may 

 not prove to be the larva of some species of ephemera, 

 He repeats this question in the Syiiona Nalurce. 



" In March and April, the females deposit their eggs 

 without any settled order, and perfectly loose in the wa- 

 ter. They appear to the naked eye like very minute 

 globules of a light brown colour. Each ovum, when 

 magnified, closely resembles the farina of a mallow. It 

 is thickly beset with spines on every side, and coated 

 over with a transparent gelatinous substance, reaching 

 just to the extremities of the spines, and is most proba- 

 bly intended to assist in causing them to adhere to the 

 substances on which they may chance to fall, or as a se- 

 curity from the attacks of smaller insects. In about a 

 fortnight or three weeks, the eggs are hatched, and the 

 young animals may be seen to swim with great liveli- 

 ness, by means of three very long pair of arms or row- 

 ers, which appear -disproportionate to the size of th 

 animal, and indeed it bears in this very small state not 

 much resemblance to the form it afterwards assumes; 

 but, in the short space of a very few hours, the body 

 assumes a lengthened form, and begin? to acquire the 

 tail-fin. The eyes in this state do not appeal - peduncu- 

 lated. On the seventh day after hatching, they approach 

 pretty nearly the form, of the perfect animal ; the}-. 



