MOLLUSCA (except CEPHALOPODA). 
141 
come mostly from Wales and Shropshire, but there are a 
few from Tyrone, and a fine series of the loosely-coiled 
Machirm from Scotland (Fig. 75 c). 
Cambrian Mollusca are few, and in Wales, where the 
rocks are exposed, the shells are poorly preserved. 
2 rrimaeva and Bellcroplion camhriensis (Fig. 75 c) may be noted. 
In a special Table-case at this end of the Gallery are placed 
together the British and foreign specimens of CONULARIDA. 
These, which are almost exclusively Palaeozoic, are some- 
times regarded as forming a Sub-Order of Pteropoda ; but 
now that the origin of the Pteropoda from Opisthobranch 
Gastropoda appears certain, this view is scarcely tenable. 
Some of the simplest forms are found in the Lower Cambrian 
of North America, and of these Salterella, Hclenia, and 
Hi/olithellus are exhibited. They are thick -walled tubes, 
straight or bent, smooth or striated, ending in a point, and 
are generally placed in a family with Torcllella from Sweden, 
which has a shell of phosphate of lime. Salterella has also 
been found in West Australia, and Ilyolitliellus occurs in 
Ordovician rocks. The Devonian Coleoprion is probably an 
allied form. The shell of Hyolithes [77icca] and a few similar 
forms is composed of carbonate of lime, is conical, straight 
or curved, triangular, elliptical, or flattened in cross section. 
Its surface is smooth or striated, and it is closed by an 
operculum. The narrow end of the shell is often divdded by 
cross partitions. Species of this genus lived throughout the 
Palaeozoic Era, but were most abundant in its earlier half. 
The shell of Tentaeulites is an elongate cone, ornamented 
with rings. It often begins in a small bulb, and the earlier 
portion may be partitioned as in Hyolithes. Its thick wall is 
composed of two layers. 
The genus abounds in 
Silurian and Devonian 
rocks, often being the 
chief constituent of cer- 
tain beds. Conularia is 
the most widely distri- 
buted in space and time, 
and contains the gi’eatest 
number of species and 
the largest individuals of 
all Conularida. The shell 
is elongate and four-sided. 
Each face is divided lengthwise by a groove (Fig. 76c) and 
Fig. 76 . — Conularia quadrisulcata, Coal 
Pleasures of Coalbrookdale. The lower 
end is broken oS. a, side view; b, 
aperture seen from above ; c, back view. 
Gallery 
VIII. 
Table-case 
16, 
Central 
Case A7. 
