MARYLAND GEOLOGICAL SURVEY 463 



DiscoRBiNA ORBICULARIS (Terqueiii). 

 Plate CXXXI, Fig. 5. 



Rosalina orbicularis Terquem, 1876, Auim. sur la Plage de Dunkerque, p. 75, pL ix, 

 fig. 4, a, b. 



Description. — Test minute, trochoid, consisting of several rotaliform 

 convolutions; marginal keel sharp, angular; superior surface conical, 

 inferior, depressed and approximately flat. The ehamhers are remark- 

 ably curved and overlap in such a way as to make it rather difficult to 

 clearly mark the several volutions. The septa are visible as grace ful 

 curved lines but are not depressed and the shell is finely porous in our 

 specimens. 



As a fossil we find it recorded in the Miocene of southern Italy and in 

 the Upper Pliocene sands of Eome. At the present time it is best known, 

 according to Brady, as a coral reef species but it is not confined to reefs. 

 It ranges in depth from the littoral zone to al3out 400 fathoms. 



Occurrence. — Choptank Formation. Jones Wharf. 



Collection. — Maryland Geological Survey. 



Genus PLANORBULINA d'Orbigny. 

 The genus Planorhulina occupies a close relationship with two other 

 generic types, namely, Truncaiulina and Anomalina. It is typically 

 characterized by its wide spreading flattened form, with coarse perforate 

 shell and it is subject to great variation in aperture, marginal fringe, 

 limbation of sutures and in sometimes possessing exogenous tubercles. 

 It is at the present time common to seas of all latitudes and occurs from 

 the littoral zone down to depths of 3000 fathoms. As a fossil it is known 

 as early as the Carboniferous, is rare in the Lias, common again in the 

 Cretaceous and is well represented throughout Tertiary time. 



PLANORBULINA MEDITERRANENSIS d'Orbigny. 



Plate CXXXI, Fig. 6. 



Planorbulina mediterranerms d'Orbigny, 1826, Ann. Sci. Nat., vol. vii, p. 280, pl.xiv, 

 tigs. 4-6; Modele No. 79. 



Description.— Test much flattened, wide-spread, consisting of a num- 

 ber of irregular vaulted chambers with depressed umbilical center. Mar- 



