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Show 366 MOLLUSCA. culum; the animal is like a true Nerita, and most generally the columella is not dentated. It inhabits fresh water. A small species, very prettily coloured, abounds in the rivers of France; it is the Nerita fluviatilis, L.; Chemn., IX, cxxiv, 1 88( 1). The columella in others, however, is finely crenulated(2), and of this number there are some in which the spire is armed with long spines-CLITHON, Mont. ( 3) . FAMILY II. CAPULOIDA( 4 ). Recent researches have convinced us that it is to the Tt·ochoida that we must approximate this family, which contains five genera, four of which are taken from the Patellre. They all have a widely opened, scarcely turbinated shell, with nei· ther operculum, emargination nor siphon; the animal resembles the other Pectinibranchiata and has the sexes separate. There is but one branchial comb transversely arranged on the roof of the cavity, and its filameJ\tS are frequently very long. CAPULus, Montf.-PILEOPsis, Lam. A conical shell with a recurved and spiral summit, which has long caused it to be placed among the Patellre; the branchire are in one range under the anterior margin of the branchial cavity; the pro· boscis is long, and there is a closely plaited membranous veil under the neck; the eyes are at the external base of the conical tenta· cula(5). The HIPPONYX, Defr. Would appear from the shell to be a fossil Capulus, very remark· (1) Add, Nerita turrita, Chemn., IX, cxxiv, 1085. {2) Nerita pulligera, Chemn., loc. cit., 1878-1879;-.N. virginca, List., 604, 606. (3) Nerita corona, Chemn, 108:1, 1084. (4~ M. rleBlainvilleplaces most ofthem among his ltermaphroditical, non-sym· metrzcal Paracephalophora,· but they all appear to me to be diwcious. (5) Patella hungarica, List., 544-32;-Pat. calyptra, Chemn., X, clxix, 1643 -44;-Pat. mitrula, Gm., List., dxliv, 31. GASTEROPODA PE.CTINIBRANCHIAT A. 367 able, boweve~, for a bed formed of calcareous matter, on which it rests, and wh1ch probably exuded from the foot of the animal( I). CREPIDULA, Lam. The shell oval, with an obtuse horizontal point, directed obliquely bac.kw~rds and laterally; the apertur~ forming the base of the shell, which .Is half clos~d beneath and behmd by a horizontal plate. The abdominal sac which contains the viscera is on this plate, the foot beneath, and the head and branchire forwards. The latter consist of a range of long filaments attached under the anterior margin of the branchial cavity. The eyes are at the external base of two conical tentacula(2). The genus PILEoLus, Sowerby, Ap~ears to consist of Crepid~l<E, in which the transverse plate occupies half the aperture; their shell, however, is more like that of a Patella(3). They are only found fossil. SEPTARIA, Fer.-NAVICELLA, Lam.-CIMBER, Montf., 82. T~e shell re~embles a Crepidula, except that the summit is symme~ rlcal and.laid on the posterior margin, and that the horizontal plate ~s less sahent. The animal is also provided with an additional, megularly shaped, testaceous p1ate, horizontally connected with the superi~r surface of the muscular disk of its foot, and covered by the abdommal sac, which it partially supports. It is probably analogous to an o~erculum, but does not exercise its functions, being, in a measure, Situated internally. The animal has long tentacula, at wh~se exte.rnal base are pedicles which support the eyes. They inhabtt the r1vers of hot countries( 4). In the ~Yl Patella cornucopiJJ, Lam., KnotT., Petrif., II, part ii, pl.131, f. 3, andiUainv. ~ualac. ~ 2 .(2) Patella fornicata, List. 545, 33, 35;-P. aculeata, Chemn., X, clxviii 1624- J;-~tl Goreensis, Martini, I, xiii, 131, 132;-P. solea, Naturf., XVIII, ii, '15;-P. crep! ua~ Adans. Seneg., I, ii, 9;-P. porcellana, List., 545, 34. J';/ .~leolus plicatus, Sowerb. ;-Pi/." lmvis, Id., Genera of Shells, No. IX;-Pii. 01 • Desb., Ann. des Sc. Nat., I, xiii, 3, a, b, c. . (4~ Patella neritoi'dea, List., 545-36, and Naturf., XHI, v, I, 2;-Pat. borbon~ · ~1'Y Saint-Vincent, Voy. I, xxxvii, 2; and for the animal, Quoy and Gaym., oy. e Freycin., pl. 71, f. 3-6. . |
