MOLLUSCA FROM JUAN FERNANDEZ AND EASTER ISLAND 223 
13, 1891), but it differs distinctly in colour and sculpture from every species 
of the genus hitherto known from the Peruvian region. 

Lunatia pisiformis Recluz. Masatierra, 20—35 m, sand and Corallina, 
3 sps., max. h. 6 mm; wh. 47/2 ('"/4); Cumberland Bay, many sps., max. h. 
5,7 mm ('/12 1916); same locality, 30—4o m, 2 small shells (1/4 1917). Previously 
known from Valparaiso (TRYON; REEVE). 
Littorina mauritiana Lamarck. — Masafuera, stones on the shore, many 
sps., max. h. 18 mm. Distribution from Mauritius to N. Zealand (TRYON, 1887, 
Man. of Conch. IX). 
Trifora basalis n. sp. PI. 8, fig. 7. — Shell elongate, uniformly grayish- 
white. (Nuclear whorls broken off.) Postnuclear whorls slightly convex; suture 
strongly impressed, marked by a fine thread. Sculpture consisting of 3 revolving 
riblets on each whorl, the uppermost narrower than the others in the 3—4 first 
postnuclear whorls, than equal in strength, crossed by strong axial ribs, forming 
rounded knobs in the crossing points and squarish pits in the interstices; 
microscopically reticulated of spiral and longitudinal striae; axial riblets in the 
third whorl 16, in the 4th 18, and in the penultimate 20. Last whorl beneath 
the three rows of knobs with a basal smooth keel, and, on its evenly rounded 
base, with 4 further similar ones, all separated by furrows narrower than the 
keels and finely sculptured by transverse striae. Aperture pear-shaped, colu- 
mella concave, canal as long as the aperture. Dimensions: height 6,3, h. of 
aperture I,7, breadth 2 mm. Postnuclear whorls 7 '/s. 
Masatierra, 20—35 m, sand and Corallina, 1 somewhat worn and frag- 
mentary shell (apex and outer lip broken off), 7/4 1917. The shell is similar 
to 7. galapagensis Bartsch 1907', which has, however, only 3 basal ridges and 
a different sculpture in the uppermost postnuclear whorls. 
Cerithiopsis dispar n. sp. Pl. 8, fig. 8. — Shell turrited, dark-brownish 
with lighter nodules; whorls convex, suture channelled, marked with a fine 
thread. Nuclear whorls 2, smooth; postnuclear whorls 12, sculptured with 3 
spiral riblets, the uppermost one somewhat narrower, crossed by axial riblets 
and nodulous in the crossing points; interstices between the tubercles smooth, 
(or nearly so), and shining. Axial riblets 15 in the third and fourth, 21 in the 
penultimate whorl. Last whorl with a smooth basal keel beneath the 3 rows 
of tubercles; base beneath this peripheral keel flattened and smooth, only with 
growth striae. Aperture ovate-rhomboid, outer lip thin; columella short, straight; 
canal oblique, short, about half the height of the aperture. Dimensions: h. 6,8, 
br. I,7, h. of aperture I,2 mm. 
Masatierra, 30—40 m, sand with Corallina, '/4 1917, 2 sps. 
On account of its smooth apical whorls this species is a true Cerzthzopsis 
(cf. BARTSCH Ig1I”), most closely related, as it seems, to 7. gloriosa Bartsch 
from California; the latter has, however, a more pronounced sculpture, especially 
its basal keel is stronger, the base is concave and the canal is much wider. 
1 The West American Mollusks of the Genus Triphoris. Proc. U. S. Nat. Mus. Vol. 33. 
2 The Recent and Fossil Mollusks of the Genus Cerithiopsis from the West Coast of 
America. Proc. U. S. Nat. Mus. Vol. 40. 
