PATELLA. 257 



** With a single branchial leaf, and the heart and one auricle, not in 

 contact with the intestine. 



This section of the Patellida comprises the typical Patella, 

 Acmtea, Calyptrtea, and Pileopsis, which have a single bran- 

 chial plume, and all but symmetrical shells. 



PATELLA, Linnaeus. 



P. PELLUCIDA, Linn. 



P. pellucida, Brit. Moll. ii. p. 429, pi. 61. f. 3, 4 ; (animal) pi. A. A. f. 1. 

 P. lavis, Auctomm. 



Shell, an obtuse symmetrical cone of variable altitudes, 

 with striae or fine ribs, and intense cerulean lines radiating 

 from the vertex, which is anteal, to the basal periphery. 



Animal when young ovately convex ; when adult, subconical 

 and often much depressed. As long as the shell maintains 

 the character of the "pellucida " of authors, it has a regular 

 figure, but as soon as adolescence has passed, then the animal 

 almost always begins to increase its circumference in a dif- 

 ferent plane, the pellucidity diminishes, and the full-grown 

 shell becomes opake, when it will be seen that the original 

 form, styled pellucida, forms the subcentral vertex of the adult 

 P. l&vis. This condition may be observed in most full-grown 

 examples, and thus declares the identity of the two forms 

 so emphatically, as to render it unnecessary to examine the 

 animals for distinctive characters. It is difficult to conceive 

 on Avhat grounds they have been separated. I have, however, 

 compared a large series, in all stages of growth, of the pellu- 

 cidan animal with the P. I avis ; it is almost needless to say, 

 the organs are similar in every respect, allowing for the varia- 

 tions of colour dependent on age. 



The mantle does not extend beyond the shell, except that a 

 cordon of about 50-65 equidistant, rather long, extremely 

 slender, sharp-pointed, white, tentacular filaments, proceeding 

 from minute eminences contiguous to the fine lead-coloured 

 line that borders its circumference, floats beyond the margin. 

 These are so fine as to require a good lens to see them : on 



s 



