BKYOZOA. 533 



bifoliate fronds, varying in width and height; thickness rarely 

 exceeding 2 mm., generally much less. Surface smooth, with cell 

 apertures sub-circular, varying but little in size, averaging 0.13 

 mm. in diameter, seven or eight in 2 mm., regularly arranged 

 in the spaces between the maculae, which usually are much the 

 largest over the basal expansion. Immediately surrounding the 

 zooecia apertures there is a narrow, slightly elevated sloping 

 space, which on the other side slopes again into the sub-angu- 

 lar mouths of a single or double series of small mesopores. 

 The latter are aggregated at intervals of about 3 mm. into 

 clusters varying much in size. Median lamina very flexuous, 

 with difficulty distinguished from the long prostrate basal por- 

 tion of the zooecial tubes. These overlap each other for a con- 

 siderable distance before they make an abrupt bend and proceed 

 direct to the surface. Walls moderately thick in the vestibular, 

 thin in the primitive region. Superior hemiseptum obsolete, in- 

 ferior, sometimes quite pronounced. Diaphragms entirely want- 

 ing, even in the mesopores. 



Position and locality: Keokuk group; Warsaw beds, War- 

 saw, 111. 



. STICTOPORELLA? UNDULATA Ulrich. 



PI. LXIX, fig. 6-66. 



The specimens upon which this species is founded are two 

 small, imperfect, undulating fronds, less than 2 cm. in height 

 and width, and about 0.5 mm. in thickness. Surface nearly 

 smooth, exhibiting a few inconspicuous elevations, the centers of 

 which are occupied by zooecia separated by slightly wider in- 

 terspaces than usual. Zooecia arranged in regular series vary- 

 ing in direction. Apertures almost circular, sub-equal, about 

 0.15 mm. in diameter, eight in 2 mm., with small mesopores 

 placed at the angles of junction. Interspaces rather thin. 



The smaller and more delicate frond, and much less numerous 

 mesopores, distinguish this form from S. basalis of the Keokuk 

 group. 



Position and locality: Chester group, Litchfield, Ky. 



