PECTEN. 217 



to receive the head of the animal ; external surface ribbed, 

 grooved, striated or banded radiately. On rocks and sea-weeds 

 in all climates. — Obs. Patelloida differs from Patella in the con- 

 struction of the animal ; Siphonaria, in the lateral siphon ; and 

 Ancylus, in the oblique twist of the axis, as well as in the nature 

 of the animal. The Patellae are marine. Fig. 229, P. Oculus. 



PATELLIFORM. {Patella, a dish \ forma, shape.) Shaped like 

 a dish, or like shells of the genus Patella. 



PATELLOIDA. Quoy and Gaimard. Lottia, Gray.— Fam. Phyl- 

 lidiana, Lam. — Descr. Patelliform, rather flat ; apex obtuse, 

 leaning towards the posterior margin ; muscular impression not 

 symmetrical, but widest on the right side near the head of the 

 animal ; central disc of a variable brown colour. On rocks 

 and sea-weeds in all climates.— Obs. The shells of this genus so 

 closely resemble Patella that it is almost impossible to make the 

 distinction from the shells alone. They are, however, generally 

 flatter, and have the apex placed somewhat nearer the posterior 

 margin. The animals are very distinct. Fig. 231, P. Antillarum. 



PATELLOIDEA, BL or patelliform shells. The third family of 

 the order Monopleurobranchiata, Bl. ; the animals of which are 

 described as depressed, flattened, covered by a wide external shell, 

 which is patelliform and non-symmetrical. This family contains 

 the genera Umbrella and Siphonaria. 



PATROCLES. Montf. A genus of microscopic Foraminifera. 



PATULAR1A. Sw. A sub-genus of « Anodontinae," Sw. thus 

 described : " Shell nearly equilateral, round or cordate ; no teeth. 

 P. ovata, Sw." Ex. Conch, pi. 36. rotundatus, lb. pi. ^37. 



PAVONIA. D'Orb. A genus of microscopic Foraminifera. 



PAXYODON. Schum. Hyria, Lam. 



PECTEN. Brug. {A comb.) Fam. Pectenides, Lam. Subostra- 

 cea, Bl. — Descr. Inequivalve, ribbed longitudinally, nearly equi- 

 lateral, with a triangular auricle on each side of the umbones ; 

 hinge linear, destitute of teeth, having a central pit containing the 

 cartilage ; muscular impressions one in each valve, large, sub- 

 central. — Obs. This genus of beautiful shells, to which the well 



