26 



MOLLUSCA. 



[Trachelipoda 



brown, beneath which the shell is often prettily mottled, che- 

 quered with brown and white, or covered with zig-zag markings, 

 and banded in some instances. 



This species is common on most of the British and Irish 

 coasts; adhering to stones and sea weed, between high and low 

 water-mark. 



Fig. 22 represents the shell in its young state. 



Genus 33 Neritina — Lamarck. 



Shell thin, external surface generally smooth, and frequently 

 covered with a strong, horny epidermis ; spire mostly very short, 

 sometimes nearly concealed, and at others obsolete ; aperture 

 semicircular ; outer lip plain, sharp, and destitute of teeth or 

 crenulations internally, but within the lower region of the aper- 

 ture, it is provided with a somewhat elongated, transverse pro- 

 minence, which seems the fulcrum for the articulation of the 

 operculum ; inner lip flattened, and reflected on the columella, 

 and placed obliquely to the axis of the shell ; edge generally 

 short, and dentated or crenulated ; as the animal increases in 

 dimensions, that part of the columellar lip is absorbed, which 

 makes it appear as having no columella; operculum testaceous, 

 semicircular, closing the aperture entirely, covered with a horny 

 epidermis, and provided internally at the lower end with a tooth- 

 like appendage, which fits into a hollow between the prominence 

 and lip. 



1. Neritina fluviatilis, pi. XVIII, f. 1, 2, 3, and pi. 

 XIII, f. 4, 5.— First Ed., pi. 43, f. 1, 2, 3. 



Neritina fluviatilis, Turton, Man., p. 13, f. 124; Alder, Mag. 

 Zool. and Bot., II, p. 117; Thompson, Ann. and Mag. Nat. 

 Hist., VI, p. 16; Lamarck, An. San. Vert., VI, pt. 2nd, p. 188; 

 Fleming, Brit. An., p. 321 ; Nerita fluviatilis, Mull, Moll., II, 

 p. 194 ; Drapernaud, Hist. Moll., p. 31, pi. 1, f. 1 ; Pfeiffer, I, 

 p. 106, f. 37, 38, 39; Fleming, Edin. Ency., VII, p. 82; lb., 

 Brit. An., p. 321 ; Brard, p. 194, pi. 7, f. 9, 10, 12; Turton, 

 Conch. Die, p. 127; Neritina fontinalis, Brard, Hist. Conch., 

 ]). 196, pi. 7, f. 11 ; Th.eodo.vus Lutetianus, De Montford, II, 

 p. 351; Da Costa, Brit. Conch., p. 48, pi. 3, f. 8; Pennant, 

 Brit. Zool., IV, p. 141, pi. 88, f. 142; Donovan, Brit. Sh., I, 

 pi. 16, f. 2; Montagu, Test. Brit., p. 470. 



Shell suboval, subpellucid; body very large; spire extremely 

 small, oblique, and lateral, consisting of two well defined volu- 

 tions, and terminating in a minutely small, slightly produced 

 apex; aperture luniform ; outer lip thin, sharp at the edge; 

 pillar lip white, flat, and very broadly reflected on the columella; 

 aperture closed by a testaceous operculum, of an orange-yellow 

 colour; whole shell covered with a brown or greenish epider- 

 mis, beneath which the surface is glossy and smooth, but longi- 

 tudinal, minute wrinkles, are observable by the aid of a strong 

 lens; beautifully streaked, spotted, or mottled, with white and 

 purplish-brown, deep umber, or pale brown, and in some in- 

 stances with spiral bands of either of those colours. Length 

 three-eighths of an inch ; breadth a quarter of an inch. 



Fig. 3 represents the operculum. 



Found in many of the slow running rivers and streams of 

 Great Britain and Ireland adhering to stones, as the Thames, 

 Humber, Tyne, and Tweed in England; the Liffey, Shannon, 

 and Bresna in Ireland ; and the Forth, Tay, and Clyde in 

 Scotland. 



Family VII — Peristomida. 

 Shell conoid, or subdiscoid, with the margins of the aperture 

 united; aperture protected by an operculum; fluviatile, and the 

 animal having the power of respiring in water. 



Genus 34 Paludina. — Lamarck. 



Shell ovate, or oblong; spire somewhat turreted; the volu- 

 tions smooth, rounded, and subcarinated ; aperture subrotund, 

 ovate, or oblong, a little angulated above, slightly modified on 

 the inner side by the gibbosity of the body volution; lips united 

 all round, with acute edges; operculum corneus, with concentric 

 lines of growth, and provided with a sublateral nucleus. 



1. Paludina vivipara, pi. XIV, f. 71, 72 First Ed., pi. 



41, f. 71, 72. 



Paludina vivipara, Lamarck, An. San. Vert., VI, pt. 2nd, p. 

 173 ; Brard, Coq. de Paris, p. 174, pi. 7, f. 1 ; Fleming, Brit. 

 An., p. 315 ; Alder, Mag. Zool. and Bot., II, p. 116; Thomp- 

 son, Ann. and Mag. Nat. Hist., p. 17; Cydostoma viviparum, 

 Drapernaud, Hist. Nat. des Moll., p. 34, pi. 1, f. 16, 17; Tur- 

 ton, Man., p. 113, f. 118; Brard, Coq. de Paris, p. 174, pi. 7, 

 f. 1 ; Rossmassler, f. 66; Helix vivipara, Montagu, Test. Brit., 

 p. 386; Brown, Wernerian Mem., II, p. 527; Viviparus fluvio- 

 rum, De Montford, II, p. 247; Paludina achatina, Sowerby, 

 Gen., f. 1. 



Shell thin, subconic, oblong-ovate; spire consisting of five 

 extremely ventricose, abruptly diminishing volutions, separated 

 by a deep suture, and terminating in an acute apex ; aperture 

 suborbicular, a little contracted above; pillar lip slightly reflect- 

 ed, behind which is a subumbilicus; inside smooth, bluish-white, 

 the external bands shining through ; whole shell covered with 

 an olive-green shining epidermis, beneath which the shell is 

 white, with three spiral, dark brown bands on the body, and two 

 on the superior volutions, which generally grow fainter as they 

 ascend, until they become nearly invisible before reaching the 

 apex ; surface slightly wrinkled longitudinally, several of which 

 are coarser than the others, marking the periodical growth of 

 the shell ; aperture protected by a thin horny operculum. 



In the young condition the shell is subglobose, subpellucid, 

 with the bands rather obscure, and the volutions appear more 

 flattened above than in the adult state. 



Found in the Thames and other slow rivers, and sometimes 

 in ponds. Plentiful in a ditch near Southport, Lancashire. 

 Occurs in a stream at Newtownards, County of Down, Ireland. 



2. Paludina achatina, pi. XIV, f. 68, 69— First Ed., pi. 

 41, f. 68, 69- 



Paludina achatina, Lamarck, An. San. Vert., VI, pt. 2nd, p. 

 174; Ency. Meth., pi. 458, f. 1, a, b; Rossmassler, p. 109, f- 

 66*; Turton, Man., p. 133, f. 119; Lymnea vivipara, Fleming, 

 Brit. An., p. 315; Cydostoma achatina, Drapernaud, p. 36, pi. 

 1, f. 18. 



Shell thin, oblong-ovate, ventricose ; spire consisting of four 

 or five considerably inflated volutions, separated by a well de- 

 fined, deep suture, and terminating in a rather obtuse apex; 

 aperture suborbicular, slightly contracted above, white within, 

 with the external bands apparent ; pillar lip a little reflected on 

 the columella ; outer lip thin, and sharp on the edge ; whole 

 shell covered with an olivaceous epidermis, beneath which it is 

 provided with three, dark reddish brown, spiral girdles on the 



