424 
MOLLUSCA. 
Genus 22. — UMBRELLA.— Lamarck. 
Generic Character. —Body of the animal very thick, some¬ 
what oval, and provided with a dorsal shell; foot large, smooth, 
and flat underneath, surrounded by a border, anteriorly notched, 
attenuated behind; head indistinct; four tentacula, the two 
upper ones thick, short, and truncated, the other two thin, and 
shaped like pedunculated crests ; having foliaceous branchiae.— 
Shell external, orbicular and somewhat irregular; 'slightly con¬ 
vex above, with the vertex towards the centre ; internal cavity 
but slightly hollowed ; lips smooth. 
Umbrella Indica. — The Indian Umbrella. 
Plate LXXXVII. fig. 24. 
Ovate, slightly convex above ; the vertex towards the centre; 
whitish, summit yellow, longitudinally striated, and concentri¬ 
cally wrinkled; inside with radiating stria}. Four inches in 
diameter. Inhabits the Indian seas. 
Genus 23. — PLE UR OB RANCH US.— Lamarck. 
Generic Character. — Body creeping, fleshy; mantle and foot 
expanded ; branchiae placed on the right side ; cloak enveloping 
the shell; neck short, contracted in some species, with an emar- 
ginate front, exhibiting the commencement of the inferior ten¬ 
tacula, the upper ones tubular and cloven; gills at the edge of 
the dorsal plait, in front of which are the generative and anal ori¬ 
fices ; mouth provided with a short retractile proboscis. 
Pleurobranchus plumida. — The Plumed Pleurobranchus. 
Plate LXXXVII. fig. 14. 
Ovate-oblong, depressed, pellucid, yellowish-white, concen¬ 
trically wrinkled, almost entirely open, rounded, and convolut¬ 
ed ; the vertex with a single turn. Half an inch long. Inhabits 
the Devonshire coast. 
TRIBE VI.-PIIYL LID I ACE A. 
The branchiae are situated beneath the margin of the mantle, in 
a longitudinal series around the body. Animals respiring in water. 
Genus 24. — PATE LLA_ Linnaeus. 
Generic Character. —Body completely covered by the shell; 
