56 GEOLOGY AND PALEONTOLOGY OF THE WEST INDIES. 



Type specimen (U. S. N. M. No. 328189) from St. Bartholomew, 

 Leeward Islands, U. S. G. S. No. 6895, spur on southeast side of cay 

 northwest of St. Jean Bay, 170 feet above sea-level; T. W. Vaughan 

 collector. 



Specimens are very numerous in this material; but a single specimen 

 was obtained showing the surface conditions with the radiating ribs. 



Although it is specifically different, this species is closely related to 

 Orthophragmina mariannensis Cushman, from Marianna, Florida. 



There appear to be from 5 to 8 layers of superimposed chambers at 

 each side of the horizontal zone of chambers as shown in the sections. 

 A few of the smallest specimens show the proloculum, but it is not well 

 developed or not sufficiently well preserved to make out its characters 

 clearly. The sections given on plate 2, figures 2 and 3, show the general 

 characters of the vertical section. 



Occasional oblique sections show the rectangular equatorial chan> 

 bers characteristic of Orthophragmina. 



This is the specimen mentioned by Vaughan as "Orbitoides sp., 

 large, stellate form" (Vaughan, T. Wayland, Carnegie Inst. Wash. 

 Year Book No. 13, p. 359, 1914). 



Orthophragmina marginata, new species. 

 (Plate 1, Figure 2; Plate 2, Figure 4.) 



The following is a description of this species : 



Test lenticular, circular, central portion strongly raised and umbonate, 

 regularly curved down to the broad peripheral flange, which is again thickened 

 near the peripheral margin; surface comparatively smooth, very slightly 

 granular, but not at all papillate. 



In vertical section the central portion is seen to be strongly biconvex, but 

 not much wider than either part of the surrounding margin-like thinner portion, 

 again thickening toward the extreme peripheral margin, which is rounded. 



Equatorial chambers small, in the center very narrow but increasing 

 slightly but gradually toward the periphery, where they are not more than 

 0.1 mm. in height. The chambers are convex on the peripheral side, almost 

 semicircular in some specimens. Lateral chambers very small and often 

 difficult to distinguish, even with an enlargement of 20 diameters (plate 2, 

 fig. 4). In the central portion there are many layers of these lateral chambers, 

 often 30 to 40 layers on either side of the equatorial band. This number 

 decreases as the convexity becomes less, and over the flattened margin there 

 are but 6 to 8 layers of lateral chambers. At the border this number is some- 

 what increased, but falls off again at the extreme outer margin. There are 

 traces of pillars in the central umbonate region, but they are not prominent. 



Diameter of the type specimen 12 to 14 mm. 



Type specimen (U. S. N. M. No. 328190) from St. Bartholomew, 

 Leeward Islands; U. S. G. S. No. 6924, from a bed of limestone on 

 point on the northwest side of St. Jean Bay; T. Wayland Vaughan 

 collector. 



