462 SYSTEMATIC PALEONTOLOGY 



POLYSTOMELLA STRIATOPUNCTATA (Fichtel and Moll). 



Plate CXXXI, Fig. 4. 



Nautilus striatopunctata Fichtel and Moll, 1803, Test. Microsc. p. 61, pi. iv, tigs. a-c. 



■ Description. — Test rounrled, convolute, both sides equally compressed 

 as in Nonionina types, peripheral margin obliquely rounded, becoming 

 somewhat lolnilated near the ultimate chamber; segments triangular, 

 twelve in the last volution, separated by nearly straight septal depressions 

 in the form of l)ridges which mark the retral jirocesses of the shell. 

 Septal plane is nearly round and the aperture is in the form of a series 

 of pores or openings along the inner margin of the ultimate segment. 



Its earliest occurrence is from the Eocene of the Paris Basin (Ter- 

 quem) . 



Occurrence. — Choptank Fokmation. Jones Wharf. 



Colleciiun. — Maryland Geological Survey. 



Family ROTALID/E. 



Genus DISCORBINA Parker and Jones. 



The typical test of Discorbina consists of a trochoid spire with nearly 

 flat base and sharp margin. Pai'ker and Jones suggested a grouping of 

 the various forms under three heads, namely, the conical, the vesicular 

 and the outspread, complanate forms. The shell is hyaline and in 

 larger forms is coarsely perforate though often small specimens and 

 certain species have small pores. The superior surface is usually raised 

 into a spire which shows the entire chambering of the shell and the arched 

 septa, while the inferior face is quite flat or even depressed and only the 

 final convolution is visil)lc. The margin is generally well defined and 

 sharp though by some few species it assumes the rounded or even 

 squarely set borders found in other types. The aperture is usually pro- 

 tected b}' an overhanging fringe and is sometimes not apparent, while 

 tubercles occur very rarely as in Asteriginse types. 



The genus does not make its appearance until near the close of (*re- 

 taceous time. In existing seas it is found in every clime being dredged 

 from Davis Strait, to the Equator and from the Equator to Magellans 

 Strait. It is more usually found in shoal waters and is quite scarce below 

 200 fathoms. 



