Gasteropoda .- 



-MOLLUSCA.- 



-Amphiperasid.e. 



335 



only, and is not retractile, as is the case in the pre- 

 vious sub-order. It varies in length and shape — in 

 some being very long, but in a great many being 

 short. The tentacles are awl-shapcd, far apart, and 

 placed on the sides of the base of the rostrum. The 

 ej-es are situated on the outer side, or behind the base 

 of these organs. The lingual membrane is often very 

 long, extending a good way into the visceral cavity of 

 the animal, and the teeth are arranged upon it in seven 

 series, 3, 1, 3. The foot of the animal varies in shape 

 a good deal. In some genera we find it expanded, 

 depressed, and formed for crawling, Platypoda ; in 

 others it is roundish, truncate, or club-shaped, Pro- 

 tfipoda; in a third set, it is compressed and adapted 

 for leaping, Leptopoda ; while in another series, it is 

 iin-lilve, and furnished with a small sucker, Heteropoda. 



Family— AMPULLARHD^E {The Apple Snails). 



The animals of this family have the rostrum pro- 

 duced, and the tentacles long and filiform. They have 

 only one well-developed gill, the left being nearly 

 rudimentary, but the mantle has a large pulmonary 

 sac on each side ; the foot is simple, and the oper- 

 culum annular and regular; the shell is sub-globose, and 

 covered with a hard, polished, olive-coloured epider- 

 mis; the mouth is entire. 



The Apple Snails are fluviatile in their habits, and 

 represent, in the ponds and rivers of the tropics, the 

 Pond Snails of more temperate climates. They live 

 chiefly in marshes, which are suliject to periodical 

 inundations, and are never found in rapid running 

 stieams. Where they do occur, it is generally in large 

 numbers, for they are abundant, and cover a large 

 space of country. They have the power of living a 

 long time out of water when the marshes dry up. 

 This faculty appears to have been first made known 

 to us by M. Caillaud, who is well known as connected 

 ■with the natural history of Egj'pt. After his return 

 to France from a residence in Egypt, he had a number 

 of si)ecimens of Ampidlaria ovata sent to him from 

 the Nile. They were packed up with a number of 

 other animals in a box filled with saw- dust. At the 

 end of upwards of four months, upon opening the box, 

 he found many of the objects in a state of putridity. 

 The contents of the bos he threw into a tub of water, 

 and next morning he was surprised to find all the 

 AmpullarijE alive, and walking about apparently in a 

 perfectly healthy state I M. Deshayes, struck by this 

 fact, and by the information he received from several 

 other travellers that these animals buried themselves 

 in the mud, and could support their existence for a 

 hngth of time when the water was dried up and the 

 mud hardened, examined several specimens with great 

 care, and found in the branchial cavity a large open 

 sac quite in the hinder part, and immediately above 

 the base of the gills. He perceived also that this 

 cavity was always full of water; and that after the 

 Snail had withdrawn itself, and tiglitly closed the 

 aperture by means of its close-fitting operculum, the 

 water is retained in this sac, and the gill thereby kept 

 in a moist and unshrivclled condition ; while, perhaps, 

 as Dr. Johnston remarks, its contact with a livujg 



surface prevents the retained fluid running into putre- 

 faction. The Apple Snails are oviparous ; the eggs 

 are large, globular, and contained in capsules. These 

 are disposed in masses, and attached to plants, &c. 

 Specimens may be seen in the collection of mollusk 

 eggs in the British Museum. The species are upwards 

 of fifty in number, and are separated into several 

 genera. The operculum, as well as the shape of the 

 shell itself, affords good generic characters. In some 

 this operculum is hoi ny, with a shelly external coat, and 

 the inner edge of the mouth of the shell is thickened, 

 so as to afford some support to the thick shelly oper- 

 culum. Such is the genus Paciiystoma — Plate 1. 

 fig. 1 — {Pachystoma solidum). Others have the oper- 

 culum simple and horny, and the edge of the shell thin. 

 Such, fcr example, is the restricted genus Ami'UL- 

 LARIA. The species of this group inhabit chiefly the 

 rivers and lakes of South America and the West 

 Indies. The South American Indians term them 

 " Idol Shells," and are said to hold them in great 

 veneration. 



Family— AMPHIPERASID^ [Poached Eggs). 



The family of Poached eggs (the genus Ovtdum 

 of Lamarck; family Amphiperasidm of Gra}') is the 

 second family of the Rostrifera. In this family, and 

 in the succeeding family of Cowries, Cyprceidce, the 

 mantle of the animal, when adult, is expanded, and 

 often reflesed over the shell, giving the surface a fine 

 polished appearance. There is no operculum. The 

 shells are involute, have a linear aperture, and a smooth 

 inner, and toothed or crenated outer lip. When young, 

 they are spirally striated, but wlien full grown, aie 

 covered with a smooth enamelled coat. The aperture 

 in many of the species is prolonged into a canal both 

 in upper and lower extremities. The species are about 

 thirty-six in number, and for the most part aie dis- 

 tributed through the warm seas of the West Indies, 

 Mediterranean, China, and West America — one or 

 two also occurring on our own coasts. They vary 

 much in shape, and have thus given origin to several 

 genera. Those which are ovate and veutricose, with 

 a narrow aperture, the extremities not prolonged iuto 

 a broad, inflexed, rounded, and crenulate outer lip, and 

 long canals, form the genus OvuLUM {Amphipcras). 

 These are the true Poached eggs, and their shells are 

 never ornamented with rich or varied colours, but are 

 usually white, pink, pale violet, or yellow, without 

 exhibiting any particular markings or pattern. Those 

 in which the shell is fusiform, with an inflexed, 

 toothed, outer lip, and the extremities of the aperture 

 produced only into short canals, form the genus Cal- 

 PURNUS. One of the species of this genus is a native 

 of the seas of the Philippine Islands, and the appear- 

 ance of the animal and its habits have been well 

 described by Mr. Adams. It is a very slow-moving 

 and sluggish creature, he says, but exhibits a singu- 

 larly beautiful and striking appearance under the calm 

 shallow water, as it glides tranquilly along the bright 

 sandy bottom. The head is pure, opaque white, with 

 the exception of one large black spot placed in the 

 centre of the forepart, which, with its large black eyes 



