268 W. H. SHERZER — THE GENUS CHONOPHTLLVM. 



hundred and twenty-five depressed convex ridges ; the grooves between them nar-, 

 row ami somewhat angular in the bottom. These ridges are gently curved in cross- 

 ing the broad flat margin of the cup. The depth of the central cavity is about 

 one inch. A transverse or horizontal section shews that many of the septa (prob- 

 ably one-half of them) reach the center. In a vertical section, extending down- 

 wards, so as to cutoff the outer extremities of a few of the radiating ridges, it is 

 shewn that the grooves on the floor of the cup indicate the position of the septa, 

 and that the ridges are the interseptal spaces. The structure, as exhibited in this 

 section, consists of excessively thin, parallel, horizontal laniinse (apparently from 

 thirty to forty in the thickness of one line). These laminae are arched upwards be- 

 tween the septa, the curve corresponding with the convexity of the radiating 

 ridges. In the lower part of the corallite, the interseptal tissue is much coarser. 

 The surfaces of the radiating ridges appear to he covered with small tubercles." 



The growth of this species varies from short, broadly explanate forms 

 to those conico-cylindrical in shape. In the latter the calyx diameter is 

 seldom over (> or 7 cm, while in the former it may reach a breadth of 22 

 or 23 cm. There is typically a central pit and broadly expanded calici- 

 nal margins : no fovea. The septa are alternating in length and vary in 

 number from 75 or 80 to 125 in adult forms. The epithecal covering, 

 structure of the septa, the dissepiments and central structure have been 

 already described in detail under the general description of the genus. 

 Billings states that "this species resembles ChonophyUum perfolialum 

 (Goldfuss), but is much larger, and has double the number of radiating 

 septa." Although in general not possessing double the number of septa, it 

 has more septa and is a larger form. The septal layers are more delicate. 

 regular and more strongly curved. Besides being found in ( 'anada 'West, 

 it has also been collected from the Upper Helderberg linn-stone- of 

 Mackinac island: falls of the Ohio ; Charleston landing; Indiana, and 

 it is occasionally met with in the drift. 



5. ChonophyUum belli, Billings. 



ChonophyUum belli, Billings. Can. Nat. and Geol., new ser., vol. ii. 1865, 



pp. 431-432. 



The types of this second species of Billings are deposited in the museum 

 of the Canadian geological survey, Ottawa, and bear the label Ptycho- 

 phyllum belli, in his own handwriting. They were assigned, however, to 

 ChonophyUum and described as follows: 



" Sub-turbinate, enlarging from a pointed base to a diameter of eighteen lines in 

 about two inches, then becoming more cylindrical. Length, three or four inches : 

 greatest diameter observed, at the cup. thirty lines. Cup, in the largest specimen 

 seen eight lines wide and six lines deep with slightly sloping walls, apparently 

 flat in the hot tom with the exception of a rough styliform projection in the center ; 

 edge of the cup narrowly rounded, a broad flat or gently convex margin all round 



