HIPPONYX. 



be France. — Diet, des Sciences Nat. v. xxi. p. 185o 



TESTA bivalvis^ adh^rens^ inaequivalvis, jequi-^ 

 latera^ impressionem muscular em in iitraque valva^ 

 forma ferri equini^ gerens; valva inferior affixa> 

 compressa^ margine plerumque elevato; valva 

 superior patelliformis^ subconica^ vertice sub- 

 marginali. Cardo edentukis. Ligamentum car- 

 diiiis nullum. 



We are not surprized that Linne, and even later writers^ 

 should have included the shells of this genus in Paidlaj 

 having been acquainted only with the upper valve. De 

 France is the first person who was able to prove that it was 

 composed of two parts, though he still considers it as an 

 unioahe^ which has tlie extraordinary property of making 

 a support^ for the purpose of raising itself above the shells 

 or stones to which it is attached, founding his opinion upon 

 what he conceives to be a difference in the nature of the 

 two valves; the upper one^ in his opinion, resembling in its 

 structure the Ci/prcea^ Volula, and other similar shells, 

 which he has observed sometimes disappear entirely in cer- 

 tain situations, where they occur in a fossil state, leaving 

 only the cast of their interior, and the impression of their 

 external parts ; and the ioc£)€r valve, bethinks, resembles in 

 its structure the Ostrea, a Genus, the shell of which, he 

 believes, never disappears in a fossil state. We cannot co- 

 incide with him in this opinion, for we see nothing in the 

 Eature of Hipponyx different from other bivalves ; on the 

 contrary, the numerous observations we have had in our 

 power to make, appear to us only to strengthen the evidence 

 in favour of the existence of a relation between this Genus 

 and Orbicula, Crania, and Terebratula ; and we suspect 

 that the animal has, in common with those genera, two 

 fringed arms or tentacula. In describing this Genus, we 



