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 onychoccllarium. 



The opesia are often without a polypidian convexity. They occur on zooecia 

 provided with many bundles of parietal muscles as in the M ' cmbraniporae. 



RECTONYCHOCELLA BILAMELLAEIA, new species. 



Plate 33, figs. 1-3. 



Description. The zoarium is free and bilQmettar. The zooecia are. hexagonal, 

 somewhat elongated, distinct or confluent through their mural rims. The crypto- 

 cyst is smooth, shallow, as long as the opesium; the opesium is oval, narrowest 

 above; the polypidian convexity is small and inconstant; the opesiular indentations 

 are symmetrical, small, and inconstant. The ovicell is endozooecial 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. 



[A0=0.18-0.24min. 

 Measurements. Opesium 01 zooecia -L 



U0=0.14-0.18mm. 



.-..,. . fAem=0.20mm. 



Upesium o onvchocellana , 



\lon- 0.10mm. 



. fZs=0.48-0.50 mm. . $ Lon=OAO-0.50 mm. 



Zooecia , Onvchocollana , 



lfe=0.36mm. Uon=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 calcined zooecium perforated by a circular 

 orifice. 



This species differs from Rectonycnocella 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 DiplopJioleos fusiforme. 



Occurrence. Upper Jacksonian (Ocala limestone) : west bank of Sepulga 

 River, Escambia County, Alabama (common) ; Old Factory, H miles above Bain- 

 bridge, Georgia (rare). 



Gotypes.CsLt. No. 63966, U.S.N.M. 



RECTONYCHOCELLA SEMILUNA, new species. 



Plate 33, figs. 9-13. 



Description. The zoarium is free, imilamellar, 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- 



