448 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



are elongated the. more the peristomice is enlarged and the more the micrometrio 

 measurements are increased. These are, therefore, often inferior to those which 

 we give above; it is not rare to observe; Zs=O.SO-1.00 by fe=0.40-0.45 mm. (fig. 8) 

 Very rarely a thin separating thread limits the zooecia (fig. 6). 



One of the distinctive characters of this species is a sort of small lyrulfi 

 which is visible on the proximal border of the apertura in the interior of the 

 zooecia (fig. 13). 



The specific character of the species is the presence of the frontal sulci at the 

 base of which the tubules open ; they give to the tangential sections an especial and 

 strange aspect (fig 15). 



Affinities. The species differs from Metradolium. obliquum in which the 

 rimule-spiramen is identical, in its frontal sulci and in its larger dimensions 

 (Zs>0.80mm). 



It differs from Metradolium transversum also provided with sulci in its very 

 large and unsymmetrical rimule-spiramen and in the almost constant presence of 

 two oral avicularia. 



Occurrence. Claibornian (Gosport sand) : One mile southwest of Eockville, 

 Clarke County, Alabama (rare). 



Lower Jacksonian (Mooclys marl) : Jackson, Mississippi (very common). 



C'otypes.Cat. No. 63850, U.S.N.M. 



ANALYTICAL KEY TO SPECIES OF METRADOLIUM. 



fSpiramen present 2. 



[No spirameu 3. 



f Large, salient lip between the spiraruen and the peristomice-. M. labratulutn. 



[No lip to the peristomice if. dissimile. 



JSmall. little distinct rimules 4. 



[Large, very distinct rimules__ 5. 



[Large, transverse peristomice, often with sulci M. transversum. 



[Small peristomice (Zje=0.10-0.12 mm.) ..-M. parvirimulatvm. 



c fLarge, symmetrical rimule, straight, rounded.. M. conveniens. 



[Large, unsymmetrical rimule, one lip being much lower than the other 6. 



Large tremopores, large micrometric dimensions M. grande. 



Small tremopores, oblique rimule M. obliquum. 



Tremopores at the base of the sulci M. sulciferum. 



Genus LEIOSELLA Canu and Bassler, 1917. 



1917. Leiosella CANU and BASSLER, Synopsis American Early Tertiary Cheilostome 

 Bryozoa, Bulletin 96, United States National Museum, p. 4S. 



The frontal is an olocyst. The peristomice of the ovicelled zooecia is of different 

 form from that of the other zooecia ; it is a lunar crescent and deprived of rimule- 

 spiramen. 



Genotype. Leiosella rostrifera Canu and Bassler. 1917. Vicksburgian. 



This genus differs from Metradolium only in the nature of the frontal which 

 is here a very thick olocyst. 



Of the three species mentioned. 'one only bears ovicells. Further researches 

 are necessarv. 



