POI.YODOXTA. 



POLYODOXTA. 



4M 



Area lortuoia. 



m, tBtrrnal rlew of a TjTe ; b, valve* clowd, the ventral or Inferior margin 

 toward! the ipecUtor ; r, rxterral view of a ralve. 



Arra antiijttara. 

 m, ralm doted. Inferior or ventral mariin toward* the npcttator. 



n. Lam, Animal rounded, more or leas thick, with no 

 tentacular filament" on the border of it* mantle ; labial appendages 

 Twrr narrow ; foot large, compressed, and alit longitudinally. 



Shell lenticular, thick, solid, rqnivalve, subequilateral, entirely 



closed ; umbonea rather small, and more or leas distant ; hinge formed 

 of a curvilinear row of small narrow, rather numerous, intrant teeth, 

 which are often incomplete under the umbonea ; ligament external. 

 (Rang.) 



The fuclunctUi live on sandy or muddy bottoms, and have been 

 (bund at depths ranging from 5 to 17 fathoms. They move by means 

 of the foot, which the animal uses to propel itself. 



The number of living species stated in the Tables of M. Deshayes 

 is 19. Woodward gives 50. 



P. pilonu. Shell orbiculato ; ovate, tumid, marked with decussate 

 stria) ; umboncs oblique ; epidermis brown, hairy. It inhabits the 

 Mediterranean and the Atlantic Ocean. (Lam.) 



Pectunculus pilonts. 



There are about 200 fossil species of the genus Area. They are 

 found in the Lower Silurian Rocks. 



Nucula (Lam.). Animal rather thick, Bubtriquetrous, having tho 

 mantle open only in its inferior moiety, with entire borders, denti- 

 culated throughout the length of the back, without posterior prolonga- 

 tions ; anterior buccal appendages rather long, pointed, stiff, applied 

 one against the other, like a kind of jaws, the posterior ones equally 

 stiff and vertical ; foot very large, delicate at its root, enlarged into a 

 great oval disc, the borders of which are furnished with tentacular 

 digitations. 



Shell rather thick, sometimes nacreous, subtriquetrous, equivalve, 

 inequilateral ; umbones contiguous, and curved forwards ; hinge 

 formed on each valve of a numerous row of small pointed t-itli. 

 disposed in a line broken under tbe umbo ; ligament in great part 

 internal, short, and inserted in a small oblique Cosset in each valve. 

 (Rang.) 



The species have been found on bottoms of sandy mud and sand, 

 both in actuaries and the open sea, at depths varying from the surface 

 to 60 fathoms. According to Mr. Cuming, tho same species vary 

 much as to the depths at which they live ; for he found N. cuneala, 

 from 14 to 45 fathoms; A', obltqua from 14 to 60 fathoms; and 

 N. Piium from 17 to 45 fathoms. 



Animal of Xucula Autlralu. 



1. a a, mantle ; 6, foot ; c, branchla ; e e, adductor mtucln. 2, Outline of 

 ahcli, with the foot of the animal projecting. 



M. De Blalnville divide* the Nuculm into two sections : 



A. Species with the border entire. Ex. If. rottrata. 



S. Species with the border crenulated. Ex. A r . maryaritacca. 



The number of recent species is 70. They are found in the seas of 

 the United Stated, Norway, the Cape of Good Hope, Japan, Sitta, and 

 Chili. The number of foseil species is about 100. 



