NUMMULITIDAE—AMPHISTEGINA; HETEROSTEGINA. 57 
Test equally biconvex; periphery acute, with a narrow carina, somewhat 
lobulate; umbilical region depressed, with a small central boss of clear shell 
material, not extending out to the general contour of the test; retral processes 
about one-fourth the width of the chamber, in depressed channels above the 
sutures, the intermediate portions being raised, inflated, gradually increas- 
ing in width toward the periphery; wall smooth, translucent, with very minute 
puncte; aperture a series of small rounded pores at the base of the apertural 
face of the chamber. 
Diameter up to 0.50 mm. 
P. advena, while not as common in this region as the two preced- 
ing species, has nevertheless been found at several stations. That it 
is not the same as Miinster’s Robulina subnodosa will be seen by a 
comparison of our species with the figures of the type of Miinster. 
While his figures are very small, the general contour of the test in 
apertural view shows the great difference between these two species. 
Miinster’s figure shows a test rhomboid in apertural view, with the 
greatest width at the umbilical region, while in our species the 
umbilical region is depressed. The specimens in the Tor‘ugas region 
are very constant in their characters. The specimens referred to Poly- 
stomella subnodosa from the general Indo-Pacific region are probably 
either P. advena or a closely allied species. 
Genus AMPHISTEGINA d’Orbigny, 1826. 
Amphistegina lessonii d’Orbigny. 
Specimens of Amphistegina are abundant at many of the stations 
in the Tortugas collection. D’Orbigny referred the West Indian 
Amphistegina to his species Amphistegina gibbosa. Many of the 
specimens from this region are thicker than is typical of those of 
some parts of the East Indies. A careful study of abundant material 
from the two general regions may show that there are distinctions 
which are constant in their character. The West Indian specimens 
are all comparatively small, none exceeding 2 mm. in diameter. 
Genus HETEROSTEGINA d’Orbigny, 1826. 
Heterostegina antillarum d’Orbigny. 
(Plate 10, Figure 5.) 
Heterostegina antillarum d'Orbigny, in De la Sagra, Hist. Fis. Pol. Nat. Cuba, 1839, “‘ Forami- 
niféres,’”’ p. 121, pl. 7, figs. 24, 25. 
There are single specimens from two stations which are Hetero- 
stegina and may be referred to d’Orbigny’s species, although they 
are not so fully developed as shown in his type figure. Heterostegina 
in the present oceans is limited to warm, shallow waters, such as are 
characteristic of coral reefs. The development in the tropical Atlantic 
is very small compared to that of the Indo-Pacific, although in the 
Eocene of the West Indian region there is a fine development of the 
genus. 
It is worthy of note here that these two specimens were from the 
two stations where the temperature is abnormally high for the region. 
