324 
BULLETIN 106;, UNITED STATES NATIONAL MUSEUM. 
BEISSELINA MIDWAYANICA, new species. 
Plate 7, figs. 1-13. 
Description. — The zoarium is a bifurcated Eschara ; the fronds are compressed, 
little thick ; the two lamellae, back to back, are inseparable. The zooecia are indis- 
tinct; the frontal is perforated with some pores irregularly placed. There is no 
peristome ; the peristomice is small and orbicular. The aseopore is large and placed 
on the median axis of the zooecia. 
,r , t-> • ^ \h/pe=0.0§ mm, 
M easurements. — Peristomice , _ 
Vlpe— 0.06 mm. 
Variations. — The frontal pores are absent (fig. 3), rare (fig. 4), or abundant 
(fig. 2). In the interior (fig. 5) the pores appear like perforations direct in the 
olocyst. The transverse sections (fig. 7) indicate some lateral walls, quite thin and 
intimately joined. On the transverse thin section the two lamellae are distinct and 
the olocystal elements are grouped in a transversal line. These elements are very 
dense, quite crowded, and it is difficult to obtain sections sufficiently transparent 
(fig. 11). The longitudinal section (fig. 12) is difficult to interpret; but our schematic 
figure is perfectly exact. 
Affinities . — This species differs from Beisselina forata in its smaller orifice 
(0.06 instead of 0.09 mm.), in its rarer and smaller frontal pores, and in the absence 
of the peristome. 
Sometimes there are some large salient avicularia with pivot as in Beisselina 
labiata Gabb and Horn, 1862, of the Vincent own marl (see plate 7, fig. 14). It 
differs from this Cretaceous species in the absence or the rarity of the large frontal 
avicularium, in the smaller diameter of its peristomice (0.06 mm. and not 0.11 mm.), 
in its smaller aseopore, and in the absence of the peristome. 
O ccmrence.- — Midwayan (Clayton limestone) : One mile west of Fort Gaines, 
Georgia (very common) ; Mabelvale, near Little Rock, Arkansas (common) ; 
Luverne, Crenshaw County, Alabama (rare). 
Cotypes . — Cat. No. 63821, U.S.N.M. 
BEISSELINA TRULLA, new species. 
Plate 43, figs. 19-21. 
Description. — The zoarium is an Eschara with wide and rounded fronds; the 
two lamellae are inseparable. The zooecia are elongated, distinct; the frontal is 
ornamented with 6 or 7 large pores of which one is an aseopore. The peristome 
is salient, thin, and sharp ; the peristomice is orbicular. 
M easurements . — Peristomice 
[lxpe=0. 11 mm.. 
\lpe= 0.11 mm. 
Zooecia 
f Lz= 0.55 mm. 
lfe=0.24 mm. 
Affinities . — This 'species is easy to recognize by its distinct zooecia and its 
frontal perforated like a colander. It differs from Beisselina implicata in the size 
of its frontal pores which attain 0.04 mm. in diameter and in its much larger 
peristomice (0.11 and not 0.06 mm.). 
