830 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



Variations. The zoaria are not always reticulate; it is frequent to find 

 branches free, smooth, or spinous. The relative arrangement of the apertura and 

 mesopores is that of Sparsicavea; the zones are almost always transversal, but 

 very irregular (fig. 3). The mesopores are sometimes closed by a calcareous 

 lamella. 



An excellent longitudinal section permitted us to study the branching of 

 the zoaria (fig. 11). At the center of the zoarium and quite distant from the 

 bifurcation, two tubes diverge, an axial tube to the left and an axial tube to the 

 right ; their successive ramifications diverge necessarily in forming the two zoarial 

 branches. 



The mesopores have a diameter almost equal to that of the tubes; this char- 

 acter is not visible in the tangential sections (fig. 13). The zones of mesopores 

 appear to be formed of branched mesopores (figs. 11, 12). 



Affinities. In its reticulate zoarium and in the aspect of its surface, this 

 species is identical with Ascosoecia ulrichi; it differs from it in its somewhat larger 

 apertura (0.12 and not 0.10 mm.). 



Occurrence. Middle Jacksonian : Near Lenuds Ferry, South Carolina (rare) ; 

 Eutaw Springs, South Carolina (very common). 



Cotypes. Cat. No. 65374, U.S.N.M. 



Genus PARTRETOCYCLOECIA Canu, 1919. 



1919. Partctrocycloecia (in error for Partretocycloecia) CANTJ, Etudes sur les Ovicelles 

 des Bryozoaries Cyclostomes (2), Bulletin Socit6 G6ologique de France, ser. 4, 

 vol. 17, p. 346. 



The tubes are club-shaped. 



Genotype. Partretocycloecia (Cavaria) dumosa Ulrich. 



Range. -Midwayan-Vicksburgian. 



All the known species of this genus have hollow zoaria (Cavaria form of 

 growth). The tubes are short and their club-shaped form does not appear very 

 clearly in transversal sections. It would be preferable to chose a genotype with 

 a solid zoarium. 



Another consequence of the contraction is to transform certain mesopores into 

 aborted tubes ; that is to say, into dactylethrae. 



PARTRETOCYCLOECIA DUMOSA Ulrich, 1901. 



Plate 103, figs. 1-14. 

 1901. Cavaria dumosa ULBICH, Maryland Geological Survey, Eocene, p. 208, pi. 59, figs. 4-8. 



Description. The zoarium is free, hollow, branched, dichotomous. arborescent. 

 The tubes are short, club-shaped, cylindrical, with their extremity bent (in section). 

 The peristomes are orbicular, hardly salient, thin, irregularly distributed in quin- 

 cunx. The mesopores are smaller, polygonal, but rounded and (in section) with 

 thick walls. The ovicell is large, smooth, perforated by the tubes; each tube is 

 accompanied by a single mesopore. 



