510 Transactions. 
expanded and conforming to the irregularities of the rock-surface. Other 
methods of attachment are a pedicel passing through a foramen in one 
valve of the shell (brachiopods), the base of the column or body-cavit 
of sea-anemones, and a byssus consisting of strong threads (Mytilidae). 
(c.) Certain adjustments of sedentary animals to the rock-surface 
may be mentioned here. Limpet-like shells have their margin irregular: 
occasionally in Cellana radians, always in Gadinia conica (fig. 7) and 
Siphonaria zelandica. e genus Crepidula provides examples in which the 
plane of the aperture is convex or concave according to the surface on which 
the species live. C. costata is usually found on rocks, and the contour of 
the peristome viewed from the side is concave; but in C. crepidula it is 
convex when within the disused shells of gasteropods, and concave when 
attached to the outside. The latter is the more usual, and shells of this 
shape are often considered to form a distinct species (C. monozyla). 
aR 
Fie. 7.—Gadinia conica, Taylor's Mistake, Shell with irregular peristome. _ 
Fic. 8. ria obl Shag Point. Shell strengthened with heavy ribs. 
G. —Sip на, 2 f 
Fro. "Vento columna, Island Bay. Sessile barnacle with tent-like form 0 
shell. 
_ Siphonaria zelandica adjusts the shape of its shell to the rock-cavity 
in which it settles. If this is a hollow which can accommodate the animal 
e es hence one-sided shells are iind 
times found. Gadinia conica is also occasionally found with the apex ne? 
