18G - 



speciniens are of enormous size. In the Ohipola and Oak Grove 

 faunas of Florida _0, haitcnsis is the most widely distributer! of 

 the- oj'Sters and is also ore sent in the Shoal ?.iver famia. (1) 

 Here it attains a larp-e size, reaching 10 or 12 cm. across. •'hen 



(1), '^-ardiier, -'t.-.A., Mssv 



compared with specimens from either Santo Dominp-o or j'lorida the 

 Bov/den forms are very small indeed. In the case of the large 

 Florida forms the Ouitline is more suhcircular, the plications more 

 persistent toward the umbo and the concentric lamellae often sub- 

 spino.re on the crests of the plications. 



This species is characterized by its subcircular or broadly 

 ovate outline and stronp-, relatively regular, sharply angular pli- 

 catinns. Tbese feat^ires rea^^ily distinguish it from the associat- 

 ed 0, m.egodon . vliich is more elongate, typically subfaleate, v/ith 

 broader, fev/er, weaker and less angular plications and without pro- 

 minent concentric laminae. The Oligocene Antip-uan 0. antiruensis 

 BroTTn (2) is heavier than the typical haitensis ; the ^olications. 



(2). Proc. Acad. Eat. Sci., Philadelphia, vol. 65, totd. 60?, 614, 

 pis. 19, fiff. 17; 20, figs. 1, 5, 6, 1915. 



v/hen present, although of almost the same number, are divided into 



