BllACHIOPODA. 



237 



FAMILY VII. DISCINIDJS. 



Shell attached by a pedicle, passing through a foramen in the ventral 

 valve ; valves not articulated ; minutely punctate. 



Animal with a highly vascular mantle, fringed with long horny setae : 

 oral arms curved backwards, returning upon themselves, and ending in small 

 spires directed downwards, towards the ventral valve. 



Fig. 161. Dorsal. Fig. 162. Ventral lobe. 



Discina lamellosa, Brod. y. 

 M, umbo; /, foramen; d, disk; a, anterior adductors; a', posterior adductors; 

 c,c', protractor sliding muscles; r, retractor muscles. The mantle-fringe is not 

 represented in fig. 162. 



DISCINA, Lamarck. 



Syn. Orbicula, Sby (not Cuvier*). Orbiculoidea (elliptica) D'Orb. 



Type, D. lamellosa, PL XV. fig. 31. (= D. ostreoides, Lam.) 



Shell orbicular, horny ; upper valve limpet-like, smooth or concentrically 

 lamellose, apex behind the centre ; lower valve flat or conical, with a sunk 

 aud perforated disk on the posterior side; interior polished ; lower valve with 

 a central prominence in front of the foramen. 



Animal transparent ; mantle lobes distinct all round ; labial folds united, 

 not extensile ; alimentary canal simple, bent upon itself ventrally, and termi- 

 nating between the mantle-lobes on the right side. There are four distinct 

 adductor muscles, as in Crania and the same number of sliding muscles, 

 viz. two pairs for the protraction and two for the retraction of the dorsal 

 valve, but some of these are probably inserted in the pedicle. The oral cirri 

 are extremely tender and flexible, contrasting with the stiff and brittle setse 

 of the mantle, which are themselves more like the bristles of certain anne- 



* The Orbicula of Cuvier was the Patella anomala, Mull (= Crania) as pointed 

 out by Dr. Fleming, in the " History of British Animals," 1828. 



