442 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



much elongated in the buried parts of the zoarium. This species then permits us. 

 according to Calvet, to determine the physiologic equivalence of the two organs. 



The size of the avicularian mandible indicates a voracious species, which did 

 not live long. 



The mucro is quite variable in form and it is sometimes a sort of very irregular 

 salient Up. 



Occurrence. Middle Jacksonian: One-half mile southeast of Georgia Kaolin 

 Co. Mine, Twiggs County, Georgia (rare) ; 3 miles north of Grovania, Georgia 

 (rare) ; Baldock, Barnwell County, South Carolina (rare) ; 18 miles west of 

 Wrightsville, Johnson County, Georgia (very rare) ; H miles southeast of Lily, 

 Dooly County, Georgia (rare). 



Jacksonian (Zeuglodon beds): Shubuta, Mississippi (rare). 



C'otypes.Cut, No. 64114, U.S.N.M. 



METRADOLIUM DISSIMILE Canu and Bassler, 1917. 



Plate 56, figs. 1-15. 



1917. Metradolium dissimile CANU and BASSLER, Synopsis American Early Tertiary Cheilo- 

 stoine Bryozoa, Bulletin 96, United States National Museum, p. 48, pi. 4, fig. 10. 



Description. -The zoarium is free, bilamellar, branching; the fronds are wide, 

 thick, distorted, or undulated, dichotomous. The zooecia are distinct, elongated, 

 elliptical. The frontal is a tremocyst with tubules resting on an olocyst with very 

 small pores corresponding to the tubules. The peristomie is deep and very oblique ; 

 the apertura is small and suborbicular ; the peristomice is orbicular; the spira- 

 men is median, more or less distant from the peristomice. There are two oral 

 avicularia symmetrically placed but dissimilar in form and size; the smaller is 

 round, simple, nonsalient; the larger is enormous, oval, salient, with pivot. The 

 ovicell is enormous, buried in the distal zooecia, hyperstomial but opening largely 

 into the peristomie, salient and globular; its peristomice has the form of a lunar 

 crescent; the ovicelled zooecia bear only a small avicularium with pivot. 



Measurements. Peristomice \hpe= 0.14-0. 16 mm. Zooecia rZs=0.74 0.76 mm. 

 (exterior) I Ipe 0.15-0.20 mm. ( exterior) \ls-OAO-0.50 mm. 



Variations. The two avicularia are often symmetrical and tubular (fig. 9), 

 especially on young zoaria (figs. 10, 11) ; there are some entire branches consti- 

 tuted in this way, but presenting here and there some normal avicularia. The 

 external micrometric dimensions are evidently smaller on the young zoaria (figs. 

 10. 11) ; the more the frontal becomes thickened the more the peristomice becomes 

 "u-ater and the more robust the large avicularia become. 



The spiramen is often replaced by a rimule-spiramen (fig. 7), a phenomenon 

 visible in the interior (fig. 12) on account of the great obliquity of the peristomie. 

 When the spiramen is quite large (figs. 2, 3), the oral avicularia disappear or are 

 much reduced; the fronds with this structure do not belong to a distinct variety 

 for it is a common occurrence to find fronds containing a mixture of such zooecia 

 and normal zooecia. 



