NORTH AMERICAN EARLY TERTIARY BRYOZOA. 211 



lated poster; the small distal canal rarely fuses with the distal zooecia (on which 

 consequently the rachis of the mandible is laid). Two or three septulae to the 

 zooecial wall. 



Measurements. Opesium of zooecia '~ 



(/o=0.16 mm. 



J, on= 0.34-0.36 mm. 

 Upesium ot onvchocellanum , 



J 7w?.=0.16 mm. 



^ . Ls=OAOmm. 



/ooooia 



. Lon=0.50mm. 

 Onvchoeollana 



Z<m=0.24-0.30mm. 



Variationft. The important character of this species is the large opesium of 

 the onychocellaria which is always longer than the zooecial opesium. This greater 

 size is above all very apparent in tangential sections (fig. 12) or in views of the 

 interior (fig. 10). At the exterior the breadth of the opesium is reduced in the 

 progress of calcification (fig. 11). but the length always remains quite evident, On 

 the same zoarium (fig. 13) one may thus observe both wide and narrow opesia. 



In the underside of the zoarium the zooecia are very irregularly convex; the 

 olocyst is covered exteriorly by a thin calcareous pellicle. Finally, it is not rare 

 to discover some zoaria incrusting other bryozoa. 



Tangential thin sections (fig. 12) show that the olocyst constitutive of the 

 zooecial walls is vacuolar. Such checks in calcification are not rare in old zoaria 

 of the Onychocellidae. 



Affinities. This species differs from Rectonyclwcella bilamellaria in its un- 

 ilamellar zoarium and in its large onychocellarian opesia. 



It differs from Diplopholeos fuftiform-e in the absence of the zooecial dimor- 

 phism, in its unilamellar zoarium, and in its onychocellarium, which does not fuse 

 with the distal zooecium. To differentiate it from this last species is often very 

 difficult, and the inexperienced student ought to abstain from any determination 

 which does not appear exact to him. 



Occurrence. Middle Jacksonian : Wilmington. North Carolina (common) ; 

 Baldock, Barnwell County, South Carolina (rare) ; Bich Hill, Crawford County, 

 Georgia (common) ; 18 miles west of Wrightsville, Johnson County. Georgia 

 (rare) ; 3i miles north of Grovania, Georgia (rare) ; Twiggs County, Georgia, one.- 

 half mile southeast of the Georgia Kaolin Co. Mine (very abundant). 

 Upper Jacksonian (Ocala limestone) : Alachua, Florida (common). 



Co-types. Cat. No. 63971, U.S.N.M. 



RECTONYCHOCELLA TENUIS, new species. 



Plate 33, figs. 4-6. 



Description. The zoarium incrusts shells. The zooecia are elongated, with 

 their mural rims confluent. The cryptocyst is very slightly developed, much shorter 

 than the opesium, very thin laterally; the opesium is large, elongated, entire, oval, 

 or elliptical. The onychocellarium is larger than the zooecium, fusiform; the distal 



