Ch. XVII] 



CHALK OF SOUTH OF EUEOPE. 



253 



France, Spam, Sicily, Greece, and other countries bordering the Mediter- 

 ranean. 



Fig. 293. 



a. nadioJitf-s radio-ms, D'Orb. {Jlippurites, Lam.) 



b. Upper valve of same. 



White chalk of Trance. 



Fig. 294 



Badiolifesfol'iaceus, D'Orb. 



Syn. Sphmrxilites agarici- 



formis, Blainv. 



White chalk of France. 



Fis. 295. 



Ilipptirites organisans, Desmoulins. 



Upper chalk : — chalk marl of Pyrenees ?* 



a. Young individual; when full grown they occur in groups adhering 



laterally to each other. 

 T). Upper side of the upper valve, showing a reticulated structure in 

 those parts, 5, where the external coating is worn otf. 



c. Upper end or opening of the lower and cylindrical valve. 



d. Cast of the interior of the lower conical valve. 



' The species called Iliiopurites organisans (fig. 295) is more abundant 

 than any other in the south of Europe ; and the geologist should make 

 himself well acquainted with the cast d^ which is far more common in 

 many compact marbles of the upper cretaceous period than the shell 

 itself, this having often wholly disappeared. The flutings, or smooth, 

 rounded, longitudinal ribs, representing the form of the interior, are wholly 

 unlike the Hippurite itself, and in some individuals attain a great size aud 

 length. 



Between the region of chalk last mentioned, in which Perigueux is 



D'Orbigny's Paleontologie FraiKjaise, pi 533. 



