580 THECIDEIDiE. 



two branches, not reflexed, and united to a small central pro- 

 cess arising from the centre of the valve. 



Species of Morrisia. 

 anomioides, Scacchi. lunifera, Phil. 



Fam. THECIDEIDIE. 



Animal with the oral arms folded upon themselves, united 

 by membrane, fringed with long cirrhi on their outer margins, 

 and supported by a complicated shelly loop. Mantle ex- 

 tending to the margin of the valves and closely adherent, the 

 margin simple, not ciliated. 



Genus ARGIOPE, Deslongchamps. 



Shell transversely oblong or semicircular, smooth or radi- 

 ately ribbed, strongly punctate ; hinge-line wide ; foramen 

 large and rounded; area flat, triangular; deltidium rudimen- 

 tary ; dorsal valve depressed, interior furnished with one 

 or more prominent sub-marginal septa ; ventral valve trun- 

 cated at the beak. Loop originating at the base of the 

 dental sockets and folded into two or more lobes occupying 

 the interspaces of the radiating septa to which they adhere 

 on their inner sides. 



Syn. Megathyris, D'Orb. 



Ex, A. decollata, Chemnitz, pi. 131, fig. 6. Shell, A. 

 decollata, fig. 6, a, 0, b. 



In Argiope the animal is attached by a tendon passing 

 out of the very large perforation below the truncated beak of 

 the ventral valve. The oral arms, united by membrane, 

 form a disk, and are folded so as to form four, or, as in the 

 sub-genus Cistella, only two lobes. 



