250 
BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
As usual in the genus, there is a pair of large, lateral septulae (fig. 7) and a 
large, distal septula (fig. 10). 
Growth is accomplished by segments irradiating from the center or from a 
bifurcation (figs. 8, 9); this is, moreover, very irregular (fig. 5). The segments 
are inserted the one into the other (fig. 10). 
The small interzooecial canals are very close together (fig. 7). 
The ancestrula is a hydrostatic and radicular zooecium (fig. 4) ; indeed only 
the larva is attached to large objects (fig. 9). There are no other hydrostatic 
zooecia. 
The pores of the inner face are at the extremity of the tubules which perforate 
the test even to the zooecia. 
Affinities. — This species differs from Lunularia claibornica in its larger micro- 
metric dimensions, its shallow pit in each vibracular condyle, and in its proximal, 
opesial border, which is quite concave and never convex. 
It differs from L. contigua which has the same arrangement of vibracula, in 
the complete absence of the entire zoarial cavity. 
All the other Lunulites forms observed have their vibracula placed in all the 
interzooecial angles and therefore can not be confounded. 
As noted before, Gabb and Horn have created the genus Oligotresium because of 
this especial disposition of the vibraculum; but we do not believe it necessary to 
adopt this genus. 
Occurrence. — Vicksburgian (Byram marl) : Vicksburg, Mississippi (rare) ; 
1 mile west of Woodward, Wayne County, Mississippi (common) ; Byram, Mis- 
sissippi (common). 
Vicksburgian (Red Bluff clay) : Red Blutf, Wayne County, Mississippi (rare). 
Plesiotypes. — Cat. No. 64255, U.S.N.M. 
LUNULARIA JACKSONENSIS, new species. 
Plate 37, figs. 19-22. 
D escription.- — The zoarium is a somewhat convex Lunulites. The zooecia are 
distinct, rectangular, disposed in radial and circular rows; the mural rim is 
salient. The cryptocyst is smooth, sunken, little developed ; the opesium is large, 
oval, enlarged at the. base. The vibracula are placed in distinct radial rows in all 
of the interzooecial angles; they are symmetrical and bear two lateral condyles. 
The hydrostatic zooecia are numerous, closed by an irregular, nonperforated olocyst. 
The inner side bears large, radial tuberose costules. 
Measurements. — Opesia 
'4(9=0.22 mm. „ . 7)3=0.35 mm. 
1 7,9=0.20 mm. Z °° eCia 73=0.35 mm. 
Affinities. — In the form of its zooecia this species is close to Lunulites fenestrata 
Gregorio 1890; it differs from it in the inner face, which is tuberculose and non- 
perforated. 
It differs from Lunularia tintinabula in its flatter zoarium and in its inner, 
side, which is tuberose and not perforated. 
