210 
BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
This genus differs from Onychocella only in the place of insertion of the 
retractor muscles of the polypide. This simple change causes a general symmetry 
of the zooecium and the onychocellarium. 
The opesia are often without a polypidian convexity. They occur on zooecia 
provided with many bundles of parietal muscles as in the M embraniporae. 
RECTONYCHOCELLA BILAMELLARIA, new species. 
Plate 33, figs. 1-3. 
D escription . — The zoarium is free and Mlamellar. The zooecia are hexagonal, 
somewhat elongated, distinct or confluent through their mural rims. The crvpto- 
cyst is smooth, shallow, as long as the opesinm; the opesium is oval, narrowest 
above; the polypidian convexity is small and inconstant; the opesiular indentations 
are symmetrical, small, and inconstant. The ovicell is enclozooecial and is an 
indistinct distal convexity. The onychocellarium is straight, fusiform; its opesium 
is oval, the point below, with a contracted and very finely crenulated posterior part. 
Measurements. — Opesium of zooecia 
|7«?= 0.1 8-0.24 mm. 
[lo = 0.1U0.18 mm. 
Opesium of onychocellaria 
rA<m=0.20 mm. 
| lon= 0.10 mm. 
Zooecia 
(Zs=0.48-0.50 mm. 
I fe=0.36 mm. 
Onychocellaria 
[Zon=0.40-0.50 mm. 
I Ion— 0.16-0.20 mm. 
Affinities and variations . — The opesium is quite variable. The form with 
polypidian convexity is shorter and the rarer, while the oval form with the proximal 
border concave is the longer (=0.24 mm) and sometimes occurs solely over an 
entire zoarium. We have observed a calcified zooecium perforated by a circular 
orifice. 
This species differs from Rectonychocella semiluna in its bilamellar zoarium and 
in the opesium of the onychocellarium which is shorter than the zooecial opesium. 
It is not dimorphous as in Diplopholeos fusiforme. 
Occurrence . — Upper Jacksonian (Ocala limestone) : west bank of Sepulga 
River, Escambia County, Alabama (common) ; Old Factory, 14 miles above Bain- 
bridge, Georgia (rare). 
Cotypes . — Cat. No. 63966, U.S.N.M. 
RECTONYCHOCELLA SEMILUNA, new species. 
Plate 33, figs. 9-13. 
Description . — -The zoarium is free, unilamellar, creeping over algae. The 
zooecia are slightly elongated, hexagonal, distinct, separated by a very small fur- 
row. The cryptocyst is convex, smooth, shallow, a little shorter than the opesium ; 
the opesium is elongated, oval, almost semilunar , entire; the polypidian convexity 
and the opesiular indentations are hardly visible. The ovicell is but little apparent. 
The onychocellarium is straight, rather large, fusiform; its opesium is oval, the 
pointed end below, always longer than the zooecial opesium, with a finely denticu- 
