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Arquivos de Zoologia

sharp. Stornach without complex folds. Pallial gonoducts with massive laminas, without chambers.

Descriptior.

Shell (fig. 12). Of medium size (up to 30 mm), turriform, apex eroded, color black or dark brown in. Protoconch not seen, Teleoconch acuminate, of about seven whorls, suture shallow, out surface almost straight. Sculpture strong spiral cords, about scvcn in penultimate whorl, between spiral cords a narrow and shallow furrow. Spiral cords with uniform undulations giving an effect of axial orthocline threads, about 15 in penultimate whorl. Periumbilical area without axial sculpture. Aperture elliptical, angled posteriorly, shallow an-teriorcanal. Peristome elear beige with some sparse dark brown spots, very thick in some specimens. Umbilicus lacking.

Head-Foot (figs 207, 208). Color homogeneous dark brown with some sparse clearest areas. Fixed specimens with uniform cover of elear mucus. Head protruding. Snout large, acuminate, base broad, anterior margin flattened, somewhat bilobed. Mouth longitudinal, antero-ventral and thickly muscular. Tentacles long, stubby, with a basal outer ommatophore. Eyes present but only visible by dissection of ommatophore. Foot of medium size, without divisions, a furrow in anterior margin of pedał glands. Columellar muscle of about 1.5 whorls.

Operculum (figs 57, 58). Somewhat circu-lar, comeous, nucleus sub-central, extemally spiral, occupies partially aperture, varies from multispiral (fig. 58) to slightly palcispiral (fig. 57). Muscle scar large, rounded, near inner maigin.

Mantle organs (figs 210, 211). Mantle border simple, without neither tentacles nor papillae. Mantle cavity of about two whorls. Siphon a smali area in left extremity with thickened muscular tissue. Osphradium very long, ridge-like, lying left margin of pallial cavity at about a half of gili length; anterior extremity posterior than that of gili. Gili very long, about same length than pallial cavity, filaments triangular, tali; tip with sharp tumed to right. Ctenidial vein norma] sized anteriorly, becomes larger forming a large sinus posteriorly; its posterior extremity suddenly narrows in insertion in auricle. Between gili and rcctum a proportionally narrow area. Pallial genital ducts runs at right margin, edged at left by large rectum. Anus siphoned, near right extremity of mantle border.

Circulatory and excretory Systems (figs 209, 210, 217). Heart charaeters and situation similar to those described for preceding species. Kidney proportionally large, about half whorl, situated in posterior-right limit of pallial cavity, about half in pallial roof and half in visceral mass. Kidney with only one lobe close to intestine; this lobe solid, richly vascularized, bordered by two flattened chambers. At left a chamber with smooth walls covered by two thin transparent membranes: posteriorly that of pericardium, anteriorly that of pallial cavity roof. At right a chamber with trans-versal folds in both sides, one of them attached to left surface of intestine. Nephrostome close to rectum, long, covered ventrally by a solid flap, flattened, with five to six tTansversal folds (fig. 210: fn); inserted at left in right border of kidney and at right in posterior extremity of outer lamina of pallial gonoduct; posteriorly inserts in posterior wali of pallial cavity, anteriorly free.

Digestive system (figs 212,215-224). Buccal mass just behind mouth (fig. 212). Jaws plates in anterior and middle borders, cut edge rounded, re-gular (figs 75, 76), a pair of smali projections in region between both jaws, each one with a radiate arrangement (fig. 75). Salivary ducts aperture near anterior region of two longitudinal folds of inner dorsal wali of buccal cavity. Odontophore muscles distinctive features (figs 218-224): 1) mlO inserted posteriorly, in m4, and not in m5; 2) ml5, differentiated muscle fibers of ventral wali of buccal mass surrounding antero-ventral region of radular sac, inserting in mlO in each side; 3) m7 absent; 4) mil originating in inner surface of subradular membranę and inserting in peribuccal wali, without connections with radula nor cartilages; 5) mila, a pair of smali muscles, origin in anterior extremity of cartilages, insertion in median region of inner surface of subradular membranę between mil origins; 6) m8 very long and narrow, origin in ven-tral wali of buccal mass (vw), insertion in radular nucleus. Radula very long, coiled in its posterior region. Radular teeth (figs 89, 90): rachidian teeth with 5 cusps, central cusp very larger (about double), no basal cusps; iateral tooth with 5 cusps, first cusp broad and undulated; second cusp broad, straight, tip rounded; inner marginal tooth spoon-like, with 3 broad terminal cusps; generally central cusp larger