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Vol. 36(2), 2001

developed closed chamber. Pallial oviduct with about half closed. Brood pouch without large fold.

Description.

Shell (figs 4-6,44). Medium size (up to 22 mm), turriform, apex eroded, dark brown with some sparse, spiral, reddish, minutę spots. Protoconch (fig. 44) only present in young specimens (from brood pouch), two whorls almost smooth, convex, rounded; spiral ribs begin gradually, becoming strong on next whorls. Junction of protoconch and teleoconch difficult to determine. Teleoconch with about five whorls; sculpture only spiral, broad cords, uniform in size, about 10 in penultimate whorl; between spiral cords a narrow and shallow furrow. Aperture elliptical, angled posteriorly, shallow anterior canal. Peristome glossy, color cream. Umbilicus absent.

Head-foot (fig. 136). Pigmented by dark successive transversal striae around snout. Other structures pale-brown in color. Other characters similar to those of preceding species.

Operculum (fig. 52). Similar to that of preceding species.

Mantleorgans(figs 139,141). Entiremantle border with well developed tentacles, morę concentrated at left extremity. Mantle cavity of almost two whorls. Pallial oviduct, rectum and anus situated as in those of previous species. Osphradium long, ridge like, thick, lying on left margin of pallial cavity, less than half of gili length, anterior extremity curved, posterior to that of gili; satellite fold absent. Between osphradium and gili a considerable space mainly in posterior region. Gili very long, about same length than pallial cavity, bearing many triangular, somewhat tali filaments, tip central, rounded. Between gili and rectum a proportionally broad, smooth area without developed vessels. Hypobranchial gland very thin. Ad-rectal sinus proportionally large, surrounding rectum.

Circulatory and excretory systems (fig. 142). Heart and kidney characters and situation similar to those of preceding species.

Digestive system (figs 137, 142, 144-149). Buccal mass, jaws (fig. 73) and salivary glands characters similar to those of preceding species. Odontophore muscles cite and characters also similar to those of anterior species (figs 145, 146, 148, 149) except subradular membranę which is opened posteriorly. Radula (figs 84,85): rachidian tooth with 7 apical and no basal cusp; lateral tooth with 6 cusps, being second larger; marginal tecth spoon-like, with 8 cusps each, outer marginal with terminal region discretely narrower than innerone. Stornach size and situation similar to that of preceding species. Stornach (fig. 147) intemally with a large, long, flattened central pad with a deep, medial, longitudinal furrow, curves at right in posterior region; crescentic ridge narrow, surround posterior half of central pad. Dorsal sorting area well differentiable (sa) at left, edged intemally by a fold “Y”-shaped, one of its branch begins anterior to esophageal opening. Two tali folds begin between intestine and style sac origins. Site of esophageal entrance and origin of digestive gland duet, intestine and style sac similar to those of previous species. Digestive gland of about three whorls posterior to stornach. Intestine characters similar to that of preceding species except in rectum that lacks transversal inner folds (fig. 143).

Genital system (figs 137, 138, 140, 142). Only females found. Characters of ovary and oviduct similar to those of preceding species. Pallial oviduct posteriorly closed at about half of its length (figs 140, 142). A chamber in posterior half of pallial oviduct in its ventral surface, opens anteriorly near posterior limit of pallial oviduct aperture, maybe a bursa copulatrix. Except this chamber no other differentiable structures. Brood pouch (figs 137,138) well-developed, situation and aperture similar to those of preceding species. Inner surface of brood pouch smooth with some folds radially disposed around its aperture, no large folds. Up to eight specimens can occur within brood pouch in different growth stages, from one to three whorls. Young specimens imbibed in yellow mucus.

Measurements (figured specimens, in mm). Holotype:18.8 by 8.6; MZSP 28692: 20.4 by 8.9; MZSP 28693: 17.7 by 7.2.

Distribution. Only known from type locality.

Etymology. The specific epithet “ci”, from Amazonian Tupy language, means “mother” (Cascudo, 1962), an allusion to parthenogenesis.

Aylacostoma tenuilabris (Reeve, 1860)

(Figs 7, 8, 31, 45, 53, 86, 150-168)

Hemisinus tenuilabris Reeve, 1860 (pl. 5, fig. 22); Ihering, 1902: 668 (fig. 4); 1909: 307; Oli-veira et al., 1981: 98.