DESCRIPTIVE CATALOGUE OF RECENT FORAMINIFERA. 305 



length until they become concentric rings; segments divided by radial 



partitions into numerous chamberlets with free communication; a single 



row of pores on the margin of the disk forms the only exterior aperture. 



Localities. Key West, Florida, and off Cape Fear (station 2623). 



ORBITOLITES DUPLEX Carpenter. 

 (Plate 51, figs, 2,3.) 



Shell thin, discoidal, slightly biconcave; primordial chamber con- 

 spicuous, globular; second chamber nearly surrounds the first; succeed- 

 ing segments rapidly lengthen and quickly become annular. Cham- 

 bers divided by septa into chamberlets, arranged in a double tier, with 

 free communication. Peripheral orifices in two rows, corresponding to 

 the double tier of chamberlets. This latter feature together with the^ 

 early annular segments, distinguish this species from others of the 

 genus. Diameter, 1 to 2.5 mm. (. to ^-inch). 



Locality. Key West, Florida. 



ORBITOLITES TENUISSIMA Carpenter. 



(Plate 52.) 



An extremely thin and delicate shell, having the form of a circular 

 disk with flat surfaces. In the arrangement of the chambers it com- 

 mences as a convoluted, planospiral, nonseptate tube; it continues with 

 a short series of spiral chambers and ends with a broad series of annu- 

 lar chambers. The spiral and annular chambers are partially divided, 

 by partitions projecting from the inner walls, into numerous chamber- 

 lets. The chamberlets of each annulus communicate not only with 

 each other but also with those of the succeeding annulus. A single 

 row of pores opens on the margin of the final chamber. Diameter, from 

 1 to 20 mm. (^ to f inch). The shaded portions in the figure are those 

 parts of the specimen still occupied by the protoplasmic substance of 

 the animal. 



Locality. Atlantic, south of Marthas Vineyard (station 2716), 1631 

 fathoms. 



Family YI. LAGENID^E. 



Test calcareous, very finely perforated; ether monothalamous, or con- 

 sisting of a number of chambers joined in a straight, curved, spiral, 

 alternating or (rarely) branching series. Aperture simple or radiate, 

 terminal. JSTo interseptal skeleton nor canal system. 



Subfamily- 



Test consists of a single chamber, either with or without an internal 

 tube. 



Genus LAGENA. 



Test monothalamous, with either an external or internal tubular 

 neck. 



NAT TVTTTS 97 - 20 



