434 MOLLUSCA. 



Thecidea, Def. 



The pedicle seems to have been incorporated with the small 

 valve(l). 



Orbicula, Cuv. 



The Orblculae have two unequal valves, one of which, that is 

 round and conical, when viewed by itself, resembles the shell of a Pa- 

 tella; the other is flat and fixed to a rock. The arms of the animal, 

 — Criopus, Poll, — are ciliated and spirally recurved like that of the 

 Lingul^e. 



The seas of Europe produce a small species. Patella anomala. 



Mull., Zool. Dan. V, 26,- Aiomia turhinata, Poli, XXX, 15; 



Brett. Sowerb., Lin. Trans., XIII, pi. xxvi, f. 1. 

 The Discix^., Lam., are Orbiculae, the inferior valve of which is 

 marked by a fissure. The 



Crania, Brug. 



Should be approximated to the Orbiculse. The arms of the animal 

 are also ciliated, but the shells have deep and round internal muscu- 

 lar impressions, that have caused it to be compared to the figure of 

 a skuU. 



One of them inhabits European seas; Anomia craniolaris, h.; 

 or Craiiia personata^ Bret., Sowerb., Lin. Trans., XIII, pi. xxv, 

 f. 3. Several are fossil; such as the Cran. antiqua, and the 

 others of which M. Hoeninghaus has given an excellent Mono- 

 graph. 



(1) Thecidea medtierranea, Risso, Hist. Nat. de la Fr. Merid., IV, f. 183;— Th. 

 radiata, Fauj. Mont, de St Pierre, pi. xxvii, f. 8. Further and more precise ob- 

 servations are requisite to enable us to class the Magas of Sowerby, the Sthigo 

 cKPHALA of Defrance, and some other neighbouring groups. 



