( 44 ) (4d ngyostomata.) 
16. Donapewra. Lam. PI. 
13, fig. 6. 
Ditto, but base more  Calcareous. Marine. 
enlarged in proportion ; Mediterranean,  In- 
summit more prolonged dian Seas. 
and curved. VY. Animal, p. 60. 
47. PLEUROBRANCHUS. Cuv. 
An oval plate. Marine. 
V. Animal, p. 60. 
48. Puanospirirrs. (1 ) 
Faujas. 
Sub-orbicular ; a spiral Maestricht. 
cord-like ridge on the in- 
ferior surface. Pl. 1, fig. 
20. : 
(1) This is one of the rarest and most singular shells found at Maestrieht, only 
three having as yet been met with. It seems impossible to determine whether it is 
an univalve or a bivalve; for although it resembles the valve of an oyster in form 
and thickness, it wants the little hollow found at the summit of that shell and 
serving to lodge the ligament which characterises the genus; neither has it any 
apparent muscular impression. If it be a bivalve, it is nearest to the genus 
Acardo of Lamark, but its spiral cord or ridge, with the absence of the hollow 
and muscular impression, lead us to conclude that it is an univalve. 
