UNIO, lil 
TY’PHIS. Montf. A genus composed of Murex tubifer, Auct. 
and other similar species, having the canal closed, and a perfo- 
rated tube between each varix, on the angulated part of the 
whorls. Fig. 397. 
UL'TIMUS. (The last.) Montf. A genus composed of Ovutum 
gibbosum, Auct. fig. 443, and other species in which the canals 
are not distinctly defined, nor elongated. This fanciful name is 
given to the genus, on account of its being described in the last 
page of the book. 
UMBILI'CUS. (A navel.) The hollow formed in spiral shells 
when the inner side of the volutions do not join each other; so 
that the axis is hollow. Ex. Helix algira, fig. 279, letter u. The 
term is also used to express any small, neat, rounded hollow. 
UM’BO. (The boss of a buckler or shield.) The point of a bivalve 
shell above the hinge, which constitutes the apex, or nucleus of 
each valve, from which the longitudinal rays diverge, and the - 
lines of growth, commencing at the minutest circle, descend in 
gradually enlarging concentric layers to the outer margin. 
The umbones will be marked-with the letter uw. in Cytherea, 
fig. 117. 
UMBRELLA. (A litile shade.) Fam. Semiphyllidia, Lam. Patel- 
loidea, Bl. Descr. Patelliform, sub-orbicular, compressed, rather 
irregular; apex slightly raised, placed near the centre; margin 
acute; internal surface with a central, callous, coloured disc, 
surrounded by a continuous, irregular muscular impression. 
Obs. This genus is known from Patella, by its continuous mus- 
cular impression. It is commonly called the Chinese Umbrella 
shell. There are several species. U. Indica, fig. 233. 
UN’DATED. (Unda, a wave.) Waved. 
UNGUI'CULATED. (Unguwis, a nail or hoof.) An unguiculated 
operculum, is one in which the layers are disposed laterally, and 
the nucleus constitutes part of the outer edge. 
UNGULINA. (Ungula, a nail or claw.) Fam. Mactracea, Lam. 
Conchacea, Bl. WDescr. Equivalve, sub-orbicular, sub-equila- 
teral, with margins entire, simple, closed all round; hinge with 
one short, sub-divided cardinal tooth in each valve, and a very 
minute additional tooth in one valve, an oblong ligamentary pit 
divided into two portions, one of which receives the cartilage, 
the external ligament immediately below the umbones; muscu- 
lar impressions, two in each valve, oblong; impression of the 
mantle entire. U. transversa, fig. 88. 
U’NICORNUS. Montf. Monoczros, Auct. in 
UNIO. (A pearl.) Fam. Nayades, Lam. Submytilacea, Bl. Deser. 
Equivalve, inequilateral, transverse, free, pearly within, covered 
with a smooth epidermis without; umbones prominent, gene- 
rally corroded; muscular impressions two in each valve, lateral, 
distant, the anterior composed of several small divisions; hinge 
