N E R I N A N E U 11 O P T E R A. 



furcate ; and the anterior femora are thick ; the ab- 

 domen is elliptic, and terminated by two setee. The 

 body of Nepa cinerca, Linnaeus, the type of the fa- 

 mily, is represented (with the limbs and anal setae cut 

 <>fi' near the base) in the article INSECT, vol. ii., p. 

 870, in which the respiratory apparatus of the insect 

 is exhibited from the invaluable work of M. Leon 

 Dufour. This insect is about two-thirds of an inch 

 long 1 , of an ashy colour, with the upper surface of the 

 abdomen red, and the anal setae shorter than the 

 body. This is a very common species, found in all 

 stagnant ponds, &c. ; it is very slow in its motions. 

 The eggs are of a curious form, each having a 

 series of terminal points, which bend upwards, and 

 form a kind of cup for the egg placed above (see 

 fig. 10, article INSECT, vol. ii., p. 834). 



The genus Ranatra, Fabric! us, having the Nepa 

 lincaris, Linnaeus, for its type, is distinguished by its 

 very narrow form, the rostrum porrected, ana the an- 

 terior thighs long. The typical species inhabits this 

 country, but is a local insect ; it is about an inch long, 

 with the anal setae as long as the body. It is beau- 

 tifully figured, with its details, in Mr. Curtis's British 

 Entomology. We have met with it in considerable 

 numbers in one of the ponds on Wandsworth Common. 



N ERIN A. A genus of molluscs established by 

 De France, but reunited to the genus Ceritklum of 

 other naturalists. 



NERITA (Linnaeus, Lamarck, Cuvier). The 

 true genus Nerita may be distinguished from the 

 Neritina by the following characters, independent of 

 its being a marine shell. It is solid, semi-globular, 

 concave beneath, and not umbilicated ; the aperture 

 is entire, semicircular; the summit very obtuse, left 

 side flattened and septiform, sharp, and often denticu- 

 lated ; the inner one slightly concave, generally with 

 granulations ; the operculum constantly calcareous 

 and subspiral, the summit of it marginal at the left 

 extremity, with one or two apophyses of muscular 

 adhesion on its posterior edge, opening as the animal 

 protrudes its body, and closely shutting when the 

 animal is at rest. These shells are never spiried, but 

 are variously striated or sculptured ; and Lamarck 

 distinguished them into the marine and fluviatile 

 species, on a consideration of the thickness of the 

 shell, which in the former is greater than in the latter, 

 and by the denticulated edge of the right side, which 

 does not exist in the second. We, however, agree 

 with those naturalists who derive a more constantly 

 distinguishing character from the external sculpture 

 of the operculurn a guide we have pointed out in the 

 leading article of CONCHOLOGV, as one to be depended 

 upon, but hitherto not sufficiently examined ; under 

 OPEHCULUM we shall enlarge upon this circumstance. 

 There are about nineteen species of marine Nerites, 

 and twenty-five species of fluviatile Nerites, or, as we 

 have separated them, Neritiiue. In the present genus, 

 as constituted by De Blainville, a well-defined 

 arrangement exists, including various genera of other 

 authors. The first division includes such as have 

 only one medial tooth on the left edge, called by 

 Oken Peloronta ; the second species have two teeth, 

 and the third three or four ; Lamarck's Neritina are 

 without any teeth. Another species forms Sowerby's 

 Pileolus. These molluscs principally inhabit the 

 Eastern and American seas and rivers, two only of 

 them being European. Fossil species are not numerous. 



NERITINA (Lamarck). A genus of molluscs, 

 see the article NEKJXA, from which it was separated 



315 



by Lamarck, on account of its being a fresh-water 

 shell, and the thinness of its texture. They are also 

 sometimes armed with long spine?, and variously 

 coloured externally. 



NETTLE. See URTICA. 



NEUROPTER A (Linnaeus). An order of winged 

 insects, belonging to the division having the mouth 

 formed with mandibles for mastication, and chiefly dis- 

 tinguished by the structure of the wings, which are 

 naked ; that is, not enclosed by elytra or tegmina,but 

 often having the anterior and posterior pairs of equal 

 size, and furnished with a great number of nerves, 

 which gives the wings the appearance, under the 

 microscope, of a piece of the most beautiful net-work ; 

 whence, indeed, the name of the order is derived, 

 neuron signifying a nerve, and pteron a wing ; the 

 membrane enclosed between these nerves is very fine 

 and transparent, often exhibiting a reflection of the 

 prismatic tints, or marked with spots or bands of va- 

 rious colours. The situation of these organs during 

 repose is various: in some they are horizontally ex- 

 tended at right angles from the body, as in the larger 

 LibellulidcE ; in others, as in the smaller species of 

 the same family, their inner surfaces are applied 

 against each other , whilst in the Perlidce they lie flat 

 upon the back, or are deflexed at the sides like the 

 roof of a house, as in Hemerobius, Psocus, &c. In 

 many species the wings are of equal size, as in the 

 dragon-flies, Panorpa, &c. ; in others the posterior 

 pair are considerably smaller than the others, espe- 

 cially in the Ephemerida ; in which, indeed, the 

 posterior wings occasionally are entirely evanescent. 

 In Nemoptera the posterior pair are much longer 

 than the anterior, and very slender. 



These insects have the head of a large or mode- 

 rate size, the eyes, which are lateral, sometimes occu- 

 pying nearly the whole of this part, of the body ; the 

 ocelli are placed on the forehead ; the latter are, how- 

 ever, wanting in some species, as in Myrmelcon, 

 (hmijlus, &c. ; the antenna? are frontal, and of very 

 different forms, being very short, and resembling a 

 fine bristle, in the Libellulidce and EphemeridcB ; 

 long and clubbed in Ascalaphus and Myrmclton ; and 

 filiform or setaceous in the others, The mouth con- 

 sists of the ordinary organs composing a mandibu- 

 lated mouth, the maxillae being very robust, and the 

 tongue well developed, in the dragon-flies. In some 

 species, as the Pcriidce, Hemerobiidte, &c., the con- 

 struction of the trophi is almost identical with that of 

 the Orthoptera. In the Ephemeridce, which are destined 

 to live but a day in the final state, the mouth is rudi- 

 mental and almost obsolete. In the dragon-flies the 

 palpi are also very minute, whilst in the Myrmelco- 

 nidcc (hey are long and slender. In the Panorpida; the 

 front of the head is prolonged into a kind of rostrum, 

 at the extremity of which the trophi are placed. 



The legs of these insects are of a moderate size, 

 flight being the chief mode of locomotion in the imago 

 state ; the legs do not acquire that degree of deve- 

 lopment which we find in some of the cursorial and 

 saltatorial species ; the tarsi vary in the number of 

 joints in the different, species, there being five in the 

 Hemerobii, Pcrla:, &c., four in the ItaphiduB, three in 

 the LibcllutcB. In all they are terminated by two 

 small hooks. The abdomen is long, cylindrical, or 

 compressed, with the segments distinct, and termi- 

 nated in the males of many species by hooks which 

 are employed during coupling. In some species both 

 sexes are provided with two or three very long and 



