346 MOLLUSCA. 
edge bearing a series of very conspicuous cirrhi, alternately longer and 
shorter, of yellow colour, annulate with olive. 
Inhabits Valparaiso. 
Figure 451, the animal, from below. 
PATELLA INSTABILIS (Gould). 
Testa olivaceo-cervina, elongata, elevata, ad latera compressa, creberrime 
radiatim striata, apice subcentrali, obtuso, castaneo: apertura oblongo- 
elliptica ; margine integro: facies interna lactea. 
Patella instabilis, Goutp; Proceed. Boston Soc. Nat. Hist., 11. 150. 
July 1846. Expedition Shells, 9. 
SneExi rather solid, elevated, the apex nearly central, compressed 
at the sides, so as to be made nearly semicylindrical, or like a gipsy’s 
bonnet, convex at base, so that while the shell rests at the middle 
upon the sides, the ends are considerably elevated. Surface shining, 
slightly furrowed by numerous, nearly regular, radiating strie ; fawn 
coloured, with a tint of olive, lighter at the strie. Aperture elongated- 
oval, the sides nearly parallel, and the ends equally rounded; margin 
entire ; interior a dead, bluish-white, the fundus chalky-white. 
Length an inch and a half; breadth nine-tenths of an inch; height 
four-fifths of an inch. 
Inhabits Oregon, Puget Sound ; Classet. 
Resembles P. compressa, but is much more solid and smooth, darker 
coloured, and with the apex more nearly central. It is quite pro- 
bable that the specimen examined may have derived its peculiar form 
from having grown attached to some cylindrical body. 
Figure 454, exterior view of the shell; 454 a, profile of the shell. 
PaTELLa conica (Gould). 
Testa parva, conoidea, elevata, valdé regularis, inornata, vel lineolis 
obsoletis radiantibus et concentricis striata ; colore luteo-cinereo: aper- 
tura rotundata, margine simplict, limbo marginal planato. 
