157 



5. Fissurella. A shield-formed, subconical univalve; 

 no spire ; the vertex perforated with an oblong opening. 

 Recent and fossil. PI. iii. fig. 5. 



6. Emarginula. An obliquely conical univalve ; the ver- 

 tex inclined, and the posterior margin notched. Recent 

 and fossil. PI. iii. fig. 6. 



7. Concholepas. An oval univalve, convex upwards ; the 

 vertex inclined on the left side ; the cavity terminating at 

 the base of the right edge with two teeth and a groove. 

 Recent. PI. iii. fig. 7. 



8. Slomatia. An oval, ear-formed univalve, with a pro- 

 minent spire ; opening ample, entire, and longer than wide ; 

 disk not perforated. Recent. PI. iii. fig. 8. 



9. Argonauta. An involuted univalve ; the spire turn- 

 ing into the opening ; very thin, with a tubercular double 

 dorsal keel. Recent, and very rarely fossil. PI. iii. fig. 9. 



10. Carinaria. A subconical univalve; flattened at the 

 sides, very thin ; the apex turned in a small spiral ; the back 

 furnished with a dentated keel ; the opening entire, oblong, 

 and contracted toward the keel. Recent. PI. iii. fig. 10. 



11. Sigaretus. An oval, flattish, and ear-formed uni- 

 valve, with a short spiral columella; the opening entire, 

 ample, longer than wide, and spread out towards the right 

 lip. Recent, and but rarely fossil. PI. iii. fig. 11. 



This shell, vrhich has been named hipponix, is considered by 

 M. de France, its discoverer, as an univalve, the animal of which 

 has the power of forming this additional portion to raise it above 

 the substance by which it is supported. 



Mr. G. Sowerby, who has given a very interesting account of 

 this shell in his valuable work on the genera of recent and fossil 

 shells, considers it as being decidedly a bivalve shell. 



It has not either cardinal ligament or hinge : and it is worthy 

 of remark, that similar muscular impressions are observable on other 

 valves which have been attributed to other species of patella. 



