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Cincinnati Society of Natural History. 



and more curved spine is formed by the posterior extremity of 

 the anterior lobe, which in this and other species of this 

 section of the genus is longitudinal rather than vertical. 

 Excepting the two ventral spines, the elevated portions of the 

 surface are coarsely granulose. The middle lobe is rounded, 

 situated about in the middle of the dorsal slope, and larger 

 than the rounded upper portion of the posterior lobe. 



The large, compressed spines, arising in the post-ventral 

 fourth of the valves, will distinguish this species from any 

 other previously described. 



Formation and Locality. — Same as the preceding. 



Ctenobolbina cavimarginata, n. sp. 

 Plate VIII, Figs. 7-9. 



Size: length, 1.35 mm.; hight, without flange, 0.72 mm., 

 with flange, 0.85 mm. ; greatest thickness (from tip to tip of 

 ventral spines), about 1.2 mm. 



In a side view the valves of this species are so much like 

 C. armata that the two forms were at first confused. Interior 

 and ventral views, however, are so strikingly different that 

 the separation of the specimens proved unusualfy easy. 

 Even on the outside the two forms present some differences. 

 Thus, the flange is thicker and more extensive, the middle 

 lobe relatively smaller, and none of the surface granulose. 

 The main distinction, however, lies in the flange. In C. 

 armata this is a simple plate, and so little developed that it 

 scarcely hides the contact edges. In C. cavimarginata, how- 

 ever, it extends considerably beyond the edge and is sup- 

 ported at regular intervals by cross-walls, so as to form from 

 ten to twelve deep rounded cavities. The end view is trian- 

 gular in both, but in C. cavimarginata the lower part of the 

 profile is much thicker than it is in C. armata. 



Formation and Locality. — Same as the preceding. 



Ctenobolbina insolens, n. sp. 



Plate VIII, Figs. 10 and 11. 



Size: Length, with flange, 1.88 mm.; without flange, 1.70 

 mm.; hight, without flange, 0.94 mm., with flange, 1.20 mm. 



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