450 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



Affinities. As the figured specimen is the only one found we are able to get 

 only an imperfect idea of this very remarkable species. The attenuation of the 

 rimule-spiramen in this species and in some other species of the same family is 

 always an indication of a reinforcement of the operculum more chitinizecl and 

 more rigid. 



The species differs from Leiosella orliiculnria in its larger micrometric dimen- 

 sions and the absence of small frontal avicularia. 



Occurrence. Vicksburgian ("Chimney rock" of Marianna limestone): One 

 mile north of Monroeville, Alabama (very rare). 



Holotype.C&t. No. 64296, U.S.N.M. 



LEIOSELLA ORBICULARIA, new species. 



Plate 01. figs. 22, 23. 



Description. The zoarium is free, cylindrical, formed of two separable 

 lamellae. The zooecia are distinct, almost orbicular; the frontal is smooth and 

 convex, formed of a very thick olocyst. The peristomice is large, orbicular, placed 

 in the middle of the zooecia; the rimule-spiramen is formed on one side by the 

 oral avicularium; the aperture is elongated, very oblique, somewhat oval, the point 

 below. On the border of the peristomie there is a large oral avicularium triangular, 

 not salient, with thin wall, provided with a pivot. There are some small frontal 

 avicularia, simple and orbicular, scattered among the peristomices. 



Measurements. Peristomice f#pe=0.20-0. 30 mm. . jZ2=0.50mm. 



(interior) I7pe=0.25 mm. ia 1^=0.40-0.45 mm. 



Affinities. Only two specimens have been found. The great difference in 

 form and position between the peristomice and the apertura is very remarkable. 

 We are ignorant of the ovicell. 



The species differs from Leiosella grandisora in its smaller micrometric dimen- 

 sions and the presence of small frontal avicularia. 



Occurrence. Vicksburgian (Red Bluff clay) : Red Bluff, Wayne County, Mis- 

 sissippi (rare). 



Holotype.C&t. No. 64294, U.S.N.M. 



Genus METROCRYPTA Canu and Bassler, 1917. 



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

 Bryozoa, Bulletin 96, United States National Museum, p. 49. 



The frontal is a tremocyst with tubules. The rimule-spiramen is wide and 

 of very little depth. Ovicell unknown. 



Genotype. Metrocrypta 'bucculenta Canu and Bassler, 1917. Jacksonian. 



The ovicell of this genus is unknown and it is therefore very doubtful that it 

 should be introduced into this family. The oral avicularium is very rare ; how- 

 ever, its presence seems to us the best character for classification. 



