388 



MANUAL OF THE MOLLUSCA. 



Family VII. — Discinid^. 



Shell attached by a pedicle, passing througli a foramen in tho 

 ventral valve ; valves not articulated ; minutely punctate. 



Fig. 195. Crania* 



Fig. 196. Discina.^ 



Animal with a highly vascular mantle, fringed with long 

 horny setse ; oral arms curved backwards, returning upon them- 

 selves, and ending in small spires directed downwards, towards 

 the ventral valve. 



DisciNA, Lamarck. 



Synonyms, Orbicula, Sby. (not Cuvier|). Orbiculoidea 

 (elliptica), D'Orbigny. Schizotreta, Kutorga. 



Types, D. lamellosa, PI. XV., Fig. 31. (=D. ostreoides, 

 Lamarck.) 



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

 concentrically lamellose, apex behind the centre ; lower valve 

 flat or conical, with a sunk and 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 terminating between the mantle-lobes on 

 the right side. There are four distinct adductor muscles as in 



» Dorsal valve, with tlie animal, seen by removing the mantle. 



t The animal as seen on the removal of part of the lower mantle-lobe ; the extremities 

 of the labial arms are displaced forwards, in order to show their spiral teniiinations : 

 V is the expanded surface of the pedicle ; the mouth is concealed by the overhanging 

 cirri. The mantle-fringe is not represented. 



X The Orbicula of Cuvier was the Patella anomaln, Mull (= Crania), as pointed out 

 by Dr. Fleming, in the " History of British Animal?," 1828. 



