GASTEROPODA OF THE EUCENE MARLS. 227 
ONUSTIDi. 
Genus XENOPHORA Fischer de Wald. 
XENOPHORA LAPIFERENS, nN. Sp. 
Plate xxxIv, Figs. 6-9. 
Onustus extensus (Sow.?) Conrad: Labels on specimens in collection at Rutgers 
College; Meek, Check List Eocene Foss., p. 11. 
Onustus , resembles O. extensus (Sowerby) Meek: Geol. N. J., Newark, 
1868, p. 732. 3 
Not Trochus extensus Sowerby: Mineral Conch., vol. 3, p. 140, Pl. 278, Figs. 2 a, b, 
and 3. 
Shell attaining a very fair size for the genus, depressed trochiform in 
outline, the apical angle being nearly 120° in most specimens. Volutions 
four to five in number, flattened in the direction of the spire, showing but 
little depression at the suture lines, even on the internal casts; outer mar- 
gin thin and acute, apparently bordered by a thin expansion, as in some of 
the living forms. Base slightly convex, flattened, or in some instances 
very moderately concave; axis solid in the shell, the casts scarcely show- 
ing a perforation at this point. Aperture acutely triangular, the lip reced- 
ing on the lower side, but extended forward along the margin of the pre- 
ceding volution on the upper side. Surface of the shell, as shown on the 
matrix, and often even on the internal casts, marked by diverging thread- 
like lines, which are strongly directed forward in their passage from the 
suture to the outer edge of the volution and are irregular, corrugated, and 
often interrupted. The surface of the volutions has been further orna- 
mented by the somewhat regular periodical attachment of small stones, and 
rarely of shells, which were almost invariably attached to the middle of the 
upper surface of the volution, and usually quite close to each other, their 
size being usually graduated according to..the width of the shell, the cica- 
trices of attachment marking the casts usually, even quite to the apex. 
This species seems to have been generally referred to Trochus extensus 
Sowerby, which comes from the London clay of England. It is, however, 
quite distinct, as seen when compared with one, as figured and described 
