PLEUROBRANCHUS. 267 
side of the body is furnished with a branchial plume, from 
which circumstance the family derives its name. The heart is 
non-symmetrical, with one auricle, and lies on the right side 
anterior, and in contact with the branchial plume; and its 
hermaphroditism being modified by congression, none of the 
Patelloid genera can receive it. The Bullide and Aplysiade 
reject the genus, from the very different disposition of the 
branchize ; neither can it be deposited in Lamellaria, in which 
we have placed the L. perspicua of Montagu, which, though 
somewhat similar in outward appearance, 1s an animal closely 
allied to the Muricide. It appears then that this aberrant 
group must be intercalated in the main line where the least 
violence is done to natural order; it is therefore fixed imme- 
diately after the Patelloid forms, as first showing that advanced 
system of reproduction termed hermaphroditism with mutual 
congression. 
PLEUROBRANCHUS, Cuvier. 
P. MEMBRANACEUS, Montagu. 
P.membranaceus, Brit. Moll. in. p.558, pl. 114. f.5; (animal) 
pl. X. X. f. 3. 
Lamellaria membranacea, Montagu. 
Animal thick, placed between two large subcircular disks ; 
the ventral one, which is the foot, is symmetrical, and in the 
specimen observed, when fully extended was 4 inches in 
diameter ; its colour underneath pale yellow, marked with a 
multitude of irregular anastomosing deeper yellow lines. The 
dorsal disk is strong and coriaceous, and an inch less in 
diameter than the ventral one; it is nearly symmetrical, 
having a sinuosity posteally and anteally, with, at about its 
centre, imbedded in the skin, a very thin, wrinkled, mem- 
branous, blush-coloured auriform shield, exhibiting a metallic 
lustre; 1ts posterior extremity is subspiral, and its use is for 
the protection of the viscera, but not of the branchial plume, 
which is without its range; the upper disk is studded with 
numerous large and smaller yellow prominent papille, and in 
