PURPURA PYRULA. 



507 



more nearly approximate the genus ClausUiit. with '. 

 which it properly should be united, as the animal is j 

 now ascertained to he precisely similar in its organi- i 

 sation. Shells of this genus are mostly terrestrial, 

 few of them attain a large size, and many of them 

 are quite minute ; their form is cylindrical, generally ' 

 thick, aperture irregular, half ovate, rounded, and '' 

 sub-angular at the lower part ; the margins nearly i 

 equal, reflected outwards, and separated at the upper ; 

 part by a thin columella lip ; the whorls at both ex- j 

 tremities nearly of an equal size, while those of the 

 body are larger and more ventricose. Some inhabit 

 America, but the greater portion hitherto described 

 are natives of Europe, many must also exist in India 

 and Africa not yet enumerated by naturalists. Only 

 one species in a fossil state is mentioned by De 

 France. 



PURPURA (Lamarck; BTJCCINUM, Linnreus). 

 This genus was blended by Linnaeus with the genus 

 liiirriiiKiii ; it is the last in Lamarck's arrangement 

 of that confused mass which presents the appearance 

 of a canal at the base of the aperture, it consequently 

 leads in order of proximity to the genera Monodon, 

 Conc/io/cpnx, Harpu, Dolium, Jincclnum, &c., in all of 

 which the canal has quite disappeared, and a notch 

 merely remains. The gradual diminution of the 

 canal, till it. became altogether obsolete, probably oc- 

 casioned Linnffius to arrange some of the species 

 with the Mnrices, and others with the Buccina ; 

 there are, however, characters which distinctly mark 

 this genus, and render it necessary to separate the 

 molluscs composing it from the arrangement, of pre- 

 vious authors. The aperture is never narrowed in 

 the middle, either by plaits on the columella, or by 

 teeth on the right side, but is always dilated ; the colu- 

 mella is smooth, flattened, and terminating in a point 

 at the base, where the notch is more or less obliquely 

 placed, and appears a little ascendant backwards. 

 The form of the shell is oval, either smooth or tuber- 

 culated, or angular on the exterior surface ; the aper- 

 ture ovate, dilated, sometimes internally grooved and 

 slightlycrenated or dentated at or near the right margin 

 which is sharp. It has a semi-lunar shaped thin, horny 

 operculum. The species of this genus probably amount 

 to sixty, a fe\v only of which inhabit the northern 

 seas. The animals of many of these molluscs secrete 

 a fluid which possesses a purple-tinged colour, but 

 one in particular famished that celebrated and costly 

 dye of antiquity, called the Tyrian purple, now super- 

 sedod by vegetable and mineral matter, at a price 

 within the reach of every one, and not inferior in 

 lustre. 



PYCNOGONUM (Muller). A genus of marine 

 aquatic arachnida belonging to the order Podosomata 

 of Leach (see ARACHMDA) having the legs as short 

 as the body, and robust, the antennae and palpi obso- 

 lete. They are parasitic upon the cetacea, the type 

 P. btila-nannn being about three-quarters of ar> inch 

 lono-, and of a whitish colour (see NYMPHON). Both 

 in resnect to their general appearance and parasitic 

 habits this genus is very analogous to that of CYAMUS 

 (which seej. 



PYKALlDyE (Leach). A very extensive family 

 of small lepidopterous insects, belonging to the sec- 

 tion Xocturna, and having the antenna: setaceous, 

 and but very seldom pectinated ; the palpi two, re- 

 curved, or four ; the thorax not crested , the body 

 long and slender ; the wings placed in a triangle in 

 repose, the anterior pair being rather elongate and 



glossy. There is considerable diversitv of appearance 

 in these moths, which were united together with the 

 Tortricida: by Latreille ; and some of these species, 

 including the type Pi/ra/ia rostra/is, Linnaeus (forming 

 the genus Hypena of Schrank), are of considerable 

 size, being more than an inch in expanse, but the 

 majority are of a smaller size. They are in general 

 active on the wing. The larva? have fourteen or six- 

 teen legs, those at the extremity of the body never 

 being deficient ; they are naked, or have only a few 

 scattered hairs. They often reside in a rolled up leaf 

 in which, having first closed up the mouth, they 

 change to pupae. Mr. Stephens has established nearly 

 thirty genera in this family, in his Illustrations of 

 British Entomoloa-v 



PYRAMIDELLA (Lamarck; TROCHUS, Lin- 

 naeus). This mollusc has been separated from 

 the genus Trochus, to which Linnaeus united it, 

 principally because Lamarck supposed it a terres- 

 trial species. The animal is, however, undescribed, 

 arid there appears no strong ground for supposing it 

 other than a marine inhabitant. The shell is sub- 

 conical, turreted without an epidermis ; aperture 

 semioval entire, and the outer lip sharp, the lower 

 part of the columella a little projecting and sub-per- 

 forated at the base, with three transverse plaits ; the 

 umbilicus enlarged ; about five living species are 

 known, which are said to inhabit the Indian and Ame- 

 rican seas. Several fossil species are known, all from 

 formations posterior to that of the chalk. 



PYRETHRUM (Smith). A numerous genus of 

 annual, biennial, and perennial herbs and shrub?, 

 mostly European. The flowers are syngenesiotis 

 and belong to Composite. The shrubby species are 

 green-house plants, and desirable as flowering in 

 winter ; the herbaceous sorts, commonly called fever- 

 few, grow any where in the open ground. 



PYROCHROIDyE (Leach). A family of he- 

 teromerous insects of small extent, belonging to the 

 section Trachelides. having the body narrowed in 

 front and depressed, the thorax orbicular or trape- 

 zoidal. The antennae, in the males at least, are pec- 

 tinated, the maxillary palpi somewhat serrated, and 

 terminated by a hatchet-shaped joint ; the abdomen 

 is elongated, and entirely covered by the elytra, 

 which are rounded behind. These insects are gaily 

 coloured, and are found in the spring months in 

 hedges, tvc. The larvae reside under the bark of 

 trees. That of Pyrochroa cocc'mea has been recently 

 described and figured in the Revue Entomologique 

 de Silbermann. The family comprises only two 

 genera, Pyrochroa, Georfrov, and Dendroidt-s, La- 

 treille, the first of which is British, and is distinguished 

 bv the antenna; of the males being simply pectinated, 

 the eyes apart, and the thorax sub-orbicular. There 

 are two handsome British species, Pyrochroa ruhens, 

 a very common species, of a fine red colour, and 

 P. coccinca, of a bright red, with a black head. 



PYROSOMA. A very singular naked mollusc, 

 whose discovery is due to M. Lesueuer ; it inhabits 

 the Mediterranean and Atlantic seas ; three species 

 are known. 



PYRULA (Lamarck ; MUREX, Linnaeus). The 

 molluscs constituting this genus, as well as many 

 other of different genera, were confounded by Lin- 

 naeus with the genus Mnrex, in the classification of 

 which he appears to have included all the shells 

 having a canal at the base, rendering it an extremely 

 incorrect and widely-extended genus. Bruguiere, 



