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 ascopore is large and placed 

 on the median axis of the zooecia. 



=.06 mm. 

 Measurements. .reristomice \ , 



(lpe=0.06mm. 



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 olocyst al 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 Beixseliiia 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 ayicularia with pivot as in Beisselina 

 labiata Gabb and Horn, 1862, of the Vincentown 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 ascopore, and in the absence of the peristome. 



Occurrence. Midwayan (Clayton limestone) : One mile west of Fort Gaines. 

 Georgia (very common) ; Mabel vale, near Little Bock, Arkansas (common) ; 

 Luverne, Crenshaw County, Alabama (rare). 



Cotypes.Cut, Xo. 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 ascopore. The peristome 

 is salient, thin, and sharp ; the peristomice is orbicular. 



lhpe=0.1lmm. . fis=0.55mm. 



Measurements. Jreristomice \ , Zooeciai, n 



(lpe=0.1lmm. U3=0.24mm. 



Affinities. This species is easy to recognize by its distinct zooecia and its 

 frontal perforated like a colander. It differs from Beisselina im.plicata 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.). 



