168 MITRIDA. 
this character. The group Cylindra has the teeth of Marginella 
and is placed near that genus by these authors ; the form of the 
shell also recalls Marginellide, and although the preponderance 
of characters accords with Mitra, it may be reasonably con- 
sidered a connecting link with Marginella. Volutomitra has 
been placed in Volutide on account of the dentition of V. 
Grenlandica, the only Arctic species of Mitra, but I have pre- 
ferred to retain it and its congeners in Mitride, because we 
know nothing of the dentition of numerous tropical species 
referred to it: Turricula and Strigatella are allied by theit 
dentition to the Olividee, and Imbricaria to the Turbinellide. 
Some of the larger species have no operculum, but it is often 
present, though small and rudimentary, on the foot of the smaller 
species. 
Shell with acute apex, usually well developed spire and 
plicate columella; for the most part destitute of epidermis, 
which is very thin, smooth and translucent when present. 
Mitta is related on the one hand with Voluta, on the other 
with Marginella; it is distinguished from the former by its 
columellar plaits, of which the largest are posterior whilst in 
Voluta they are anterior, by its form, and the apex, which is 
never papillary; from Marginella it is distinguished by its much 
longer spire, less polished surface , generally larger size and par- 
ticularly by wanting the thick marginal varix of the lip. 
Mirra, Lamarck. 
Syn.—Thiarella, Swains. Mitraria, Raf. Mitrolites, Krug. 
Isara and Ziba, H. and A. Ad. 
Distr.—Over 200 sp. Tropical and subtropical, but a few 
small species being found in the colder latitudes. Bathymetri- 
cally they range from low-water to eighty fathoms, the smaller 
species being usually found along shore-lines. About a hundred 
fossil species have been described, commencing with the creta- 
ceous period. JM. episcopalis, Lam. (lv, 36). 
Shell fusiform, thick; spire elevated ; aperture small, narrow, 
notched in front; columella transversely, somewhat obliquely 
plicate; outer lip thick, smooth within, not variced externally. 
The animal of Mitra has in general a very short foot, straight 
and continuous from side to side in some species, but in others 
notched and produced, with a thickened anterior margin. It is 
commonly narrow and rounded, or acuminated posteriorly, and 
it often bears a very small semitransparent horny opercuium, in 
some instances scarcely visible. The siphon is mostly directed 
forward, and the somewhat short, tapering tentacles have the 
eyes either situated about half-way, or they are placed on the 
outer side of the base. The head is long and very flat, and the 
tentacles are very close together at their bases. The proboscis 
