258 



AVOCET. 



The body of the animal is generally much coin- 

 pressed ; the mantle divided through the whole of its 

 circumference, except along the back, and furnished 

 on its unattached edge with a double row of very 

 short tentacular cirrhi ; the foot is rather small and 

 channelled, and has abyssus. The mouth is surrounded 

 with fringed lips, in addition to two pair of labial 

 appendages ; it possesses a large strong adductor 

 muscle, and two pair of small retractile muscles of 

 the foot. The shell is inequivalve, with a sinus, or 

 singular notch in the left valve, through which the 

 byssus passes ; the hinge is linear, with one primary 

 tooth on each valve, beneath the apices, which are 

 oblique, small, and not projecting. The substance of 

 the shell is thin and very fragile in some species, and 

 in others thick and ponderous ; the interior pearly in 

 the centre, with a broad black border surrounding it, 

 and the margin terminated in a fringe, formed by the 

 epidermis or foliaceous texture of the exterior ; the 

 ligament is more or less external, and contained in a 

 groove, sometimes enlarged towards the summit ; it' 

 has a very large posterior muscular impression, and a 

 very small anterior one. Lamarck had formed his 

 genus Meleagrinn from two species of Avicula, but suf- 

 ficient reason exits to unite them, as the difference of 

 their specific characters is not so strongly defined as to 

 constitute a well-grounded distinction. 'De Blainville 

 forms two subdivisions, embracing these differences ; 

 the first includes the species but slightly oblique, 

 nearly round, nacreous, vert/ thick, with the auricles 

 nearly equal, but little salient, and without teeth at 

 the hinge, forming Lamarck's genus Pintadina, which 

 he also sometimes calls Melcagrina, and Leach's 

 genus Margarita ; the second contains such species 

 as are of a thin texture, oval, oblique, with auricles 

 strongly developed, particularly the superior one, and 

 one tooth on the hinge, as in the A. macroptera, here 

 figured in its young state." 



A. Macroptera. 



Of the two species of the first division, one, the 

 Avicufa margaritifera (Mytilus margaritiferus of Lin- 

 naeus) produces that costlybut modest gem, the highly 

 coveted pearl. Some others of this genus produce 

 these isolated deposits of nacreous matter, but none 

 of such beauty and high price ; they are only found 

 in the Oriental seas, while most of the others inhabit 

 the South American seas, and one of the number is 

 found in the Mediterranean. 



There arc fifteen species known in a recent state, 

 and De France enumerates twelve fossil Avicula, and 

 three Pintad'mte, or a genus nearly allied to them. 



This genus is arranged in De Blainville's Malaco- 

 logy, in the third family, Margaritacea ; order, La- 

 mcllibranchiata ; class, Acephalophora. 



Tho Avicula margaritifera, or Mother of Pearl 

 Oyster, as it is generally called, is so familiar to every 

 one, as affording that beautifully iridescent substance, 

 of which numberless elegant trinketsand other orna- 



ments are formed, that it needs no particular descrip- 

 tion to most of our readers. It may, however, be 

 proper to state, that its iridescent character depends 

 on the striated surface of the shell ; and even when a 

 new surface is given by grinding the shell, the same 

 ffect is still produced. We are indebted to Sir D. 

 Brewster for a knowledge of this curious fact, and 

 our artizans, availing themselves of the discovery, 

 lave produced the iridescent character of mother of 

 icarl, by simply ruling the surface of polished metal. 

 AVOCET Recurvirostra. A genus of birds be- 

 onging to the order GraUidee, or waders, and much 

 more strictly deserving the name than very many 

 others to which it is applied. Their form, their habits, 

 and their principal haunts, are all so peculiar, that they 

 are a very distinctly marked as well as a very singular 

 and curious genus. 



They are birds of considerable size ; their bodies 

 are handsomely formed ; and their plumage, which 

 is remarkably ck)se and glossy, is generally pure 

 white and black, which increase the apparent inten- 

 sity of each other by their contrast, and give the birds 

 a very clean appearance. The legs are very long, 

 but they arc proportionably strong and well-jointed, 

 and they are so well adjusted to the centre of gravity, 

 that the birds walk in a firm and stately manner, and 

 have great command of themselves. The hind toes 

 are little more than rudimental . but the three front 

 ones are well formed, firm and elastic, so that the 

 bird can rise upon them as springs, when such a move- 

 ment is necessary. They are half-webbed ; but the 

 webs are of a peculiar form ; and they are fitted for 

 walking upon soft and oozy surfaces, and not for 

 swimming. In the middle of the interval between 

 every two toes, the web extends barely to half the 

 length of the toes, but it extends from thence in a 

 straight line to each toe as far as the insertion of the 

 claws ; so that half the foot has an entire web, join- 

 ing all the toes, and the other half has a triangular 

 lobe pointed in front, upon both sides of the middle 

 toe, and upon the inner sides of the others. This, 

 as already hinted, is not a swimming structure, be- 

 cause the lobes are most deficient at those places 

 where their effect in swimming would be greatest ; 

 and we find that swimming birds which have lobed 

 feet, as, for instance, the grebes, always have the 

 largest lobes toward the points of the toes. But the 

 feet of the avocet answer well for walking upon soft 

 surfaces, and equally well upon surfaces having dif- 

 ferent degrees of softness. If the place on which it 

 walks is very sludgy, the bird plants the breadth of 

 the foot, which by affording a base of considerable 

 extent, prevents it from sinking ; and if the place is 

 hard and firm, or covered with gravel, which last is 

 an unpleasant surface on which to place a foot which 

 must bear on the web, the bird can spring on the 

 comparatively free fulcra of the toes, or there even 

 find points of rest between the nodules of the gravel. 

 Among all the curiously varied structures of the feet 

 of birds, there is not one better adapted to the place 

 in which the creature finds its food than the foot of 

 the avocet. Upon an emergency, too, it can wade to a 

 considerable depth without wetting a feather ; for the 

 tarsi are long ; and the tibiae are bare of feathers to 

 nearly half their length. The muscles which move 

 the legs, though not clumsily bulky, are very strong 

 and compact, so that the bird can wade a long time 

 in water or in sludge without being fatigued. 



The neck of the avocet is long and flexible, but at 



