METOPTOMA. GASTEROPODA. 67 
TRIBE III. — PHYLLIDIACEA. 
The branchie of the animals situated beneath the margin 
of the mantle, in a longitudinal series around the body ; they 
respire in water. Shell simple. * 
Genus 1X. — PATELLA. — Linneus. 
Generic Character. — Shell ovate or oblong, more or 
less of a conical form, sometimes, although rarely, pyramidal, 
vertex rarely central, generally placed anteriorly, with its 
apex inclined towards the head of the animal ; concave 
within, and the margin entire; muscular impressions dis- 
tinct, and same form as the shell, placed about half way 
betwixt the summit and the margin, interrupted in front, 
where the head of the animal is situated; externa] surface 
striated, or ribbed, in a variable manner, from the apex to 
the base, in the latter case, the margin is variously dentated 
or crenulated. 
Patella striata. Plate IV. fig. 17. Found in the Lon- 
don Clay at Stubbington, and at Valognes and Hautville, 
France. 
This is a marine genus, consisting of numerous species, for the most part 
subject to great variety of form, depending on the local situation in which 
they are placed. They are met with on the coasts, adhering to stones and 
rocks. Their geographical range is very wide, being found in almost all 
climates. 
Fossil species are however not common, and occur only in the Great Oolite, 
the Calcaire-grossier, and in the Crag of England. 
Genus X. — METOPTOMA. — Phillips. 
Generic Character. — Shell subconical, depressed ; ver- 
tex subcentral; face under the apex truncated, general form 
somewhat shield-shaped. 
Metoptoma pileus. Plate V. fig. 18. Found in the 
Mountain Limestone Bolland. 
The shells of this genus are entirely fossil, and are at once distinguished 
from the Patelle by their truncated end. 
