MONODONTA. 65 
MI'TRA. Lam. (Mire.) Fam. Columellaria, Lam. Angyosto- 
mata, Bl. Descr. Oblong, thick, covered with a light brown 
epidermis; spire long, turrited, acute; aperture emarginated 
anteriorly ; outer lip thickened ; columella with several oblique, 
thick plaits. Obs. The pretty small shells composing this genus 
differ from Marginella, not only in general form but in the outer 
lip not being reflected. They are varied in colouring, which is 
generally rich, and also in form, some being angulated, some 
plicated, some coronated, some smooth. Fig. 431, M. Plicaria. 
Fig. 432, Conohelix marmorata, Sw. 
MITREU'LA. Sw. A genus consisting of Mitra Fissurella, casta, 
Olivezeformis, and similar species. 
MITRE’OLA. Sw. One of Mr. Swainson’s divisions of the genus 
Mitra, Auct. Described as having the apex slightly thickened. 
MODIOLA. Lam. (Modiolus, a little measure.) Fam. Mytilacea, 
Lam. Descr. Equivalve, oblique, cuneiform, inequilateral, thin, 
with the anterior side short and narrow, slightly gaping to admit 
the passage of a byssus, and the posterior side elongated, broad, 
sub-quadrate; hinge thin, toothless, rectilinear, with along, partly 
external ligament; muscular impressions two in each valve; 
palleal impression irregular, not sinuated. Obs. This genus 
differs from Mytilus, to which the common muscle belongs, in 
the anterior margin being rounded out beyond the umbo, which 
in Mytilus is terminal. The Lithodomi may be known from 
this genus by their cylindrical form. Fig. 160, M. Tulipa. 
MOLLUSCA. (From Mollis, soft.) 'The twelfth class of inverte- 
brated animals, Lam. including all soft animals with univalve 
shells, or none; divided into the following orders: Pteropoda, 
Gasteropoda, Trachelipoda, Cephalopoda, Heteropoda, fig. 220 
to 488. The term Mollusca is used in a general sense to denote 
all the animals that come under the type Malacozoa, BI. 
MONEY COWRY. Cyprza Moneta, which passes current in 
some parts of Africa. 
MONO'CEROS. (Movos, monos, single ; kepas, ceras, horn.) Fam. 
Purpurifera, Lam. Descr. Ovate, thick, covered with a brown 
epidermis; spire short, consisting of few whorls ; aperture oval, 
emarginated anteriorly; columella rather flat; outer lip thick, 
with a prominent tooth near the anterior extremity. Obs. This 
genus resembles Purpura in every respect, except in having the 
tooth from which the name is derived. 
MONOCONDYLA’A. D’Orbigny. A sub-genus of Uniones de- 
scribed as equivalve, inequilateral, sub-rotund or angulated ; 
hinge consisting of a large, obtuse, round cardinal tooth in each 
valve, with no lateral teeth. Monocondylea, (Unio) Paraguay- 
ana, D’Orb. fig. 149. 
MONODON’TA. Lam. Opontis, Sow. A genus separated from 
Trochus, Auct. on account of the tooth or notch with which 
the columella abruptly terminates. M. labeo, fig. 366. 
K 
