FAMILY 2. SEMIPHYLLIDIANA. 5] 
obliquely ovate, flat, and somewhat ear-shaped, being convex superiorly ; 
the vertex is situated near the edge, and bent inwards ; and the margin is 
entire. 
Kzample. 
Pl. CLIV. Fig. 1 and 2. 
PLEUROBRANCHUS MEMBRANACEUS, Fleming. Sowerby, Genera of Shells, 
No. 35. 
UMBRELLA, Lamarck. 
Testa externa, dorsalis, orbicularis, planulata; superné convexiuscula, 
albida, vertice minimo, subcentrali ; inferné concaviuscula, disco 
centrali, fusco-colorato, impressione musculari irregulari, continua, 
ad centrum circulariter imbuta. 
The genus which we have now to consider appears to have been first 
proposed by Lamarck under the title of Acardia; but as this appellation 
had been used by Bruguiére in reference to another class of animals, he 
subsequently abandoned it for that of Umbrella. It was not, however, 
until some time afterwards that the genus Umbrella was recognized by 
Cuvier ; for although he admitted that the shell, which had been long 
known as the ‘‘ Parasol Chinois,” appeared to differ from the Patella, he 
cautiously refused to allow it a generic distinction until the nature of its 
animal became known. The anatomy of the Umbrellz was subsequently 
described by De Blainville ; his description was rather incomplete at the 
time, but it has been since perfected by Deshayes. 
An error was committed some years since by De Blainville in the 
formation of a new genus under the title of Gastroplax, from a specimen 
of Umbrella that had its shell artificially cemented to the ventral disc ; 
and as many authors have taken considerable pains to expatiate upon 
this error, even after he had acknowledged it as such in his ‘ Manuel de 
Malacologie,’ we shall here do him the justice to quote his own words : 
H 2 
