PAL.£OXTOLOG Y. Ill 



deep, siphonal depression in the peripheral circumference of the 

 cell bottoms, which are broad, rising into a strong cone carinated 

 by the radial lamellae uniting on its apex in somewhat twisted 

 manner. Number of lamellae in specimens of four ce: : r^rs 

 cah-x diameter, from 85 to go, and at the margins of the cai \ces an 

 equal number of small rudimentary- folds are intercalated. 



Found in the upper Helderberg strata of Mackinac, at the Falls 

 of the Ohio, at Port Colbome, in Canada, and frequently in the 

 drift deposits. 



Plate XL. — The upper tier represents various silicified specimens 

 found in the drift, left-hand and lower central specimen ; the other 

 two are from the Falls of the Ohio. The right-hand specimen exhib- 

 its the invaginated, conical diaphragms almost extending across the 

 whole width of the stems, surrounded only by a narrow peripheral 

 area. 



LITH05TR0TI0X. Flemmixg. 



Compound poh-paria, formed of cjlindrical stems, enveloped bj- a 

 perfect epithecal wall, and either loosely approximated, with cir- 

 cular orifices, or intimately united, and joining under polygonal 

 outlines by mutual pressure. Structure very similar to Clisio- 

 phyllum. The outer area is divided into small cellulose spaces 

 by the interposition of vesiculose, transverse plates between the 

 vertical lamellae ; the inner area, which is not defined from the outer 

 area by an intenening wall, is formed by diaphragms reflected into 

 large protruding cones, carinated by the radial crests uniting on 

 them and invaginating into one another. The laterally compressed, 

 crest-like apices of the invaginated cones grow together and form 

 a continuous, thin axal lamina pervading the whole length of the 

 corallum. 



LITHOSTROTIOX MAMILLARE. Edwards & Haime. 



LiTHOSTROTION PROLIFERUM, Hail. 



Large colonies of remote, cylindrical stems, from one to two and 



a half centimeters in diameter, multiplying by gemmation from 

 the margins of the cahxinal disks, or astraeiform masses of inti- 



