216 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



(/(o=0.20 mm. (measuring only to the poly- 

 Measurements.-Opesium of _ pidian convexi(y) 



iCia U0=0.15mm. (without the opesiules) 



\Lz= 0.40 mm. 

 Aooecium , . _. 



[Zs=0.30mm. 



Opesium of i Aow=0.20mm. 

 onychocellaria Zopn=0.10 mm. 



Variations. The zooecia with the small opesium () are not regularly smaller 

 than the others; we can not therefore employ the nomenclature used by Harmer 

 for the Steganoporellidae. The reduction of the opesium is due to the enlarge- 

 ment of the cryptocyst; we must therefore suppose that the parietal muscles are 

 inserted there higher in consequence of the development of an organ of which 

 .we know nothing. This organ can be neither the ovary nor the testicles, for we 

 have observed ovicells in both forms of zooecia. 



The fusion of the small distal canal of the fusiform onychocellarium with the 

 cryptocyst of the distal zooecia is so general that we may now consider its char- 

 acter as distinctive upon first examination. The marginal zooecia are unprovided 

 with polypidian convexity and lateral opesiules. 



The zoarium sometimes creeps over algae. The unilamellar specimens often 

 arise primarily from incrusting specimens which are detached from their sub- 

 stratum. 



The mural rim and the cryptocyst are formed of the same elements secreted 

 by the endocyst. These elements are grouped in radiating series around the 

 opesium (fig. 14). 



Affinities. This species differs from Diplopholeos sagittellarium and from 

 D. sagittarimn by the form of its ouychocellarium, by the fusion of the distal canal 

 with the cryptocyst of the distal zooecium, and by its larger zooecial dimensions. 



When the zooecial dimorphism is not apparent, this species much resembles 

 Rectonychocella semiluna; but it is distinguished from it by its incrusting zoarium 

 and its very distinct, nearly complete opesiules. 



Occurrence. Middle Jacksonian (Castle Hayne limestone) : Wilmington, 

 North Carolina (common). 



Upper Jacksonian (Ocala limestone) : Old Factory, 1-1- miles above Bainbridge, 

 Georgia (common) ; Bainbridge, Georgia (very rare) ; 4 miles below Bainbridge, 

 Georgia (common) ; 7 miles above Bainbridge, Georgia (common) ; West bank of 

 Sepulga Eiver, Escambia County, Alabama (common) ; Chipola River, east of 

 Marianna, Florida (common) ; 9 miles north of Ocala, Florida (common) ; Plant 

 System Railroad wharf at Bainbridge, Georgia (rare). 



Cotypes.Cat. Nos. 63979, 62582, U.S.N.M. 



