298 OSTREID^. 



(cxxxii, 3). Fossil, 46 sp. L. Oolite — Chalk ; United States, 

 Europe. 



ALECTRYONiA, Fischer de Waldheim, 1825. (Lopha, Bolten, 

 1198. Dendostrea, Swainson, 1840. Actinostrea, Bayle.) Shell 

 plicate, strongly so towards the margins ; adherent partly by 

 recurved spinous processes clasping the limbs or roots of trees, 

 as mangroves, etc. O.frons, Linn, (cxxxi, 19). 



GRYPH^A, Lamarck, 1801. (Pycnodonta, Fischer, 1835.) 

 Shell free or very slightly attached ; left valve with a prominent 

 incurved umbo; right valve small, concave. Fossil, 30 sp. 

 Liassic — Cretaceous; Eur., India, U. S. 0. angulata, Lam. 

 (cxxxii, 4). 



GRYPH^osTREA, Conrad, MSS. Shell thin, elongate, straight, 

 narrow; lower valve rather deep and smooth; upper valve flat 

 or slightly concave, and ornamented with distant, regular, thin, 

 concentric laminae; beak of lower valve contorted, or turned to 

 one side ; cartilage-pit narrow, oblique. In perfectly preserved 

 specimens the typical species, 0. vomer ^ throws out long, slender 

 auricular appendages (one on each side) from the lower valve 

 near the beak. They are usually broken off, but appear to have 

 attached the species. 



