UMBRELLA. 



Lam. 



TESTA externa, orbicularis, subirregularis, pla- 

 nulata, supern^ eonvexiuseula, albida, vertiee 

 minimo, subeentrali; marginibus aeutis; in- 

 terna facie subconcava, disco centrali, calloso, 

 colorato; impressione musculari irregularis con- 

 tinua. 



Apparently very distinct from the other patelliform 

 shells, both in the characters of the shell and those of 

 the animal ; De Blainville, who alone has examined the 

 animal, must have been deceived by some accidental 

 circumstance which detached the shell from its back and 

 turned it downwards, as we think Lamarck has satisfac- 

 torily demonstrated : the name of Gastroplax, which De 

 Blainville gave to the animal in consequence of this cir- 

 cumstance, must therefore be abandoned ; and his idea 

 that the creature was contained between two valves, or 

 between a single valve and the rock, must fall to the 

 ground. In other respects De Blainville's observations 

 are interesting and satisfactory ; he has shown that the 

 animal is nearly related to the Aplysiae. Its shell, which 

 is placed on the back and serves as a protection for the 

 viscerae, is orbicular, rather irregular and flat : above 

 rather convex, whitish, with a very small, nearly central 

 vertex; its edges are sharp; the lower or inner surface is 

 concave, with a central, callous disk, which is most com- 

 monly of a yellowish or fulvous colour: the muscular 

 impression continuous all round the inside of the shell, at 

 about half way between the margin and the vertex; it is 

 very irregular. 



We are only acquainted with a single species of this 

 Genus, which is commonly called the Parasol Limpet in 



