.M.\i;'i I. \ Ml (JKULUtiJCAL SURVEY 245 



chambers inflated, elli])tieiil, <iiiliiaeiiig; surface smooth with definite 

 septal depressions; ajierlin'c iiiaiinnillatc; diameter, 0.35 mm. 



Tliis species occurs aluiiHlantly in the New Jersey Cretaceous Init the 

 t'oi-iiis ai-c iinuli lai'Lici' lliaii in llie Eocene of Maryland. 'I'lie species 

 also (1CCU1-S in tin' l'ainnnl<cy fdriMatinn o\' Virji-iiiia on the Pamunkey 

 Kwvv. 



This form is recorded IVom the Tjowcr Lias (Blake); Septaria Clays of 

 Ccnnany (Eeuss) : Cault of Folkestone (Chapman); Lower Eocene of 

 r(\<i\\cll r)ay (IWiri'ows); ]?ed Chalk of Yorkshire, etc. (Burrows, Sher- 

 horn and Bailey): and many other references. 



Pohjworpliina commvnis is closely related to Poli/inurphina prohlntia, 

 and Professor Brady thinks that they should he united under one name 

 of P. prohlrmn and the name communis he allowed to drop. Li the 

 original models described by d'Orbigny (Nos. Gl and 62), the forms 

 portrayed represent clearly distinct species, the first P. prohlema shows 

 about seven definite segments which are much inflated and with deep 

 sntures while P. communis presents about four or five segments with 

 less excavated sntures. 



In d'Orbigny's great monograph on the Vienna Basin, both forms are 

 included and the rather unimportant distinctions here seem to be that 

 P. communis is of smaller size, the superior end acnminate and the su- 

 tures are complanate while P. prohlema shows an obtuse anterior, exca- 

 vated sntnres, larger size and more inflated chambers. 



Reuss considered in his notes on Herr von Schlicht's Septaria-clay 

 Foraminifera that P. communis is a variety of P. prohlema and his con- 

 clusion may be accepted ultimately, though for the present, it seems 

 better to keep them distinct. 



Both forms have a wide distribution throughout all oceans but are 

 apparently limited to a depth of less than 155 fathoms and so are shal- 

 low water forms. It is also interesting to note that in the fossil world 

 they^ frequently occur side by side and are variously described from the 

 same localities. 



The genus Pohjmor pinna is represented by a good many forms of 

 Foraminifera as compared with other types but they never become 

 abundant as do some of the involute genera. 



