138 EOCENE MOLLUSCA. 
MARGINELLA EBURNEA, Desh. 1830. En. Meth. (Vers), vol. ii, p. 413, No. 13. 
= — Bronn. 1831. Ital. Tertiargeb., p. 18, No. 53. 
— — Desh. 1824-37. Deser. des coq. foss., &e., vol. ii, p. 707, t. 95, 
figs. 14—16, and 20—22. 
_ — J. Sow. 1850. Dixon’s Geol., &c., of Suss., p. 107. 
—_ ? Phil. 1851. Paleeontographica (Tert. Foss. Magd.), vol. i, p. 79, 
No. 174. 
_ a ? Beyrich. 1853. Die Conchyl. des Norddeutschen tert., vol. i, 
p- 52, t. 2, figs. 9 a, b. 
Nec. — _ Grat. 1838. Cat. Zool., &c., de la Gironde, p. 50, No. 478. 
nec. — — Grat. 1845. Conch. foss., &c., de Adour, t. 1, (Tarriére, &e.,) 
figs. 38—40, 
nec. — — Sismon. 1847. Syn. meth., &c., Pedemont. Foss., p. 42, No. 46. 
M. testé parva, ovato-elongatd: spird acuminata, ultimo anfractu breviori ; anfractibus 
conveaiusculis, ad suturam confluentibus ; apertura angustd ; labro posticé sinuato, extus 
marginato, intus mutico ; columella quadriplicatd. 
Shell small, elongated, with an elevated pointed spire, rather shorter than the 
aperture, and formed of five or six narrow, slightly convex whorls, somewhat depressed 
round the sutural margin, the sutures concealed by the enamel ; body-whorl conoidal ; 
aperture elongated, narrow, obscurely notched in front ; lips nearly parallel ; outer lip 
with a wide and moderately deep sinus at the suture, thickened and presenting a raised 
border along the outside margin, smooth within; columella nearly straight, and fur- 
nished with four narrow, almost equal folds, the front two of which are more oblique 
than the others. 
M. Deshayes, when he separated J/. hordeola, suggested at the same time that it 
might be only a variety of the present species; Dr. Beyrich in fact maintains the 
identity, and that the only distinction is the difference of size. I do not concur in this 
opinion. Both species belong to a group, in several of which the characters depend, 
to a great extent, on the condition of the aperture and the general form of the shell ; 
characters in some instances difficult to define, but which strike the eye forcibly, and 
from their constancy acquire specific importance. The general form of the shell in 
M. hordeola is not so broad as that of JZ. eburnea, owing to the whorls being less 
convex ; the spire is more obtuse, and comparatively shorter; and the aperture is 
longer and narrower, particularly at the posterior extremity, and it is more contracted 
at the middle in consequence of the greater involution of the outer lip. Other species 
occur in the calcaire grossier, belonging to this group, and hitherto undescribed, but 
which, as I learn from M. Deshayes, will be described in the forthcoming supplement 
to his ‘ Description des coquilles fossiles,’ &c. One of these (JZ. contabulata), appears 
to be intermediate in size between JZ. ehurnea and M. hordeola, and, in fact, to present a 
close general resemblance to the former. It is unnecessary to enter upon any examination 
