248 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



two to every two zooecia. The inner side is chitinous or very little calcified and 

 bears small tuberosities. 



Measurements : 



Opesium r#0=0.15mm. Opesium jA0=0.30mm. 



of small zooecia lZ0=0.17mm. of large zooecia i?o=0.26 mm. 

 fZs 0.35mm. . fZ2=0.40mm. 



Small zooecia { fe=0>34r _ .40mm. Large zooecia ) fe=0 _ 50mm . 



Variations. The zoarial organization of this species is analogous to that of 

 Lunulites di-stans Lonsdale, 1845, with this difference, however, that the zooecia are 

 quite calcified on their basal side (fig. 4). The concave molds (figs. 2. 4) show 

 this remarkable character very well. The convex casts which have lost the frontal 

 wall of the zooecia (fig. 1) show the internal side of the inner face of the zoarium; 

 the rows between the partitions are ornamented with numerous tuberosities. in 

 which character the species does not differ from L. distans Lonsdale. 



Another characteristic of this species is its zooecial dimorphism, which is 

 unique in this genus. We are ignorant of the function of the large zooecium. 



Vibracula are not placed in all of the interzooecial angles, as in most of the 

 species of Lunularia; there is only one for two zooecia in this way namely, that the 

 circular rows with vibracula alternate with circular rows without vibracula. Gabb 

 and Horn have proposed the genus Oligotresium for this special character. We 

 can not believe that the simple elongation of the small distal canal in which the 

 vibraculum may be lodged is a sufficient generic character. 



Lunularia vicksburgensis Conrad 1847, presents the same arrangement of the 

 vibracula, but L. contigua differs in its zooecial dimorphism. 



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

 Carolina (rare). 



PlesiotypesCat. No. 63999, U.S.N.M. 



LUNULARIA (OLIGOTRESIUM) CLAIBORNICA, new species. 



Plate 13, figs. 13-15. 



Description,.- The zoarium is a convex, expanded Lunulites, formed of radial 

 rows of zooecia and vibracula. The zooecia are ogival, transverse, distinct: the 

 mural rim is very thick; the cryptocyst is small, finely granular. The opesium 

 is semilunar and surrounded by a small collar; the proximal border is a little con- 

 cave or convex. The ovicell is a distal convexity often covered by the external 

 calcification. The vibracula are elongated, elliptical, disposed in radial rows in 

 the interzooecial angle for two zooecia; joined between them by a small canal; its 

 opesium is narrowed in the lower part by a calcareous lamella, which ends in two 

 condyles. On the inner side the radial rows are convex and pierced by large closely 

 arranged pores. 



ffl0=0.17 mm. . lLz=O.Z(} mm. 



Measurements. Opesium^, ., Zooecium , - .- 



170=0.16 mm. ,1 Js=OAOmm. 



(7>=0.30mm. 

 Vibraculum , 



I /?'=0.18mm. 



