446 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



Measurements. Apertura \ka=Q.ll nun. Peristomicef^/?c=0.18 mm. 



(interior) )Z=0.11 mm. (interior) 7/?e=0.12 mm. 



. I 0=0.50-0.60 mm. 

 Zooecia.' A OA A 1A 



1/3=0.30-0.40 mm. 



Variations. The peristomice is quite variable in its general form: it is often 

 provided with a rimule-spiramen (figs. 17, 18). but there are some entire fronds 

 which are. entirely without it (fig. 20). The ovicells are quite variable in form 

 and size (figs. 17-19). The two oral avicularia are symmetrical (fig. 20). but very 

 often there is only one large oval avicularium with pivot, having its beak turned 

 outward (fig. 19). 



The longitudinal section (fig. 21) shows that the ovicell is almost as large as 

 the zooecium itself, and that the apertura of the ovicelled zooecium is smaller than 

 that of the other zooecia. 



Affinities. The symmetry of the rimule-spiramen is very characteristic and 

 permits one to easily distinguish this species. 



It differs from Metradolium grand e. in which the rimule-spiramen is often 

 symmetrical, in its smaller micrometric dimensions (LsO.QO and not 0.90 mm.) 

 and its smaller and more numerous tremopores. 



It differs from Metradolium.: disshnile. in which the rimule-spiramen is vaguely 

 symmetrical, in the absence of zooecia with spiramen, and in the somewhat smaller 

 dimensions (Lz=0.60 and not 0.76 mm.). 



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

 Carolina (very common). 



Cotypcs. Cat. No. 64119, U.S.N.M. 



METRADOLIUM OBLIQUUM, new species. 



Plate 57. figs. 4-10. 



Description. The zoarium is free, bilamellar, erect; the fronds are fiat, bifur- 

 cated ; the two lamellae are back to back and inseparable. The zooecia are elon- 

 gated, very little distinct ; the frontal is thick, convex ; it is formed of a tremocyst 

 with tubules surmounting an olocyst, which is very thin and finely perforated with 

 corresponding pores. The apertura is oblique, suborbicular; the peristomice is 

 formed of a subcircular anter with poorly defined outlines and of an unsymmetrical 

 rimule-spiramen oblique with respect to the zooecial axis. The ovicell is globular, 

 salient, hyperstomial, largely open into the peristomie. deeply embedded in the distal 

 zooecium ; it is covered with tremopores like the frontal ; the peristomice is large, 

 transverse, in the form of a lunar crescent, of which the convexity is proximal. 

 Two avicularia are symmetrically placed on each side of the rimule; the larger is 

 salient, transverse, oval, provided with a pivot, its beak turned outward. 



Measurements. Apertura 1 , Peristomice), 



. . f?a=0.15mm. . !foe=0.15mm. 



(interior )J (exterior) I 



. (Zz=0.70-0.80mm. 

 Zooecium^ 



lfe= 0.40-0.50 mm. 



