668 GEOLOGICAL SURVEY OF IOWA. 



In many weathered specimens the exterior cellular portion is worn away, leaving 

 the interior cylindrical portion entirely separated by a vertical line. 



This fossil is one of the most widely distributed corals of the Carboniferous 

 limestones, and appears to hold the same geological position from Central Iowa to 

 Alabama, everywhere- marking the horizon of the St. Louis limestone. Being an 

 abundant and conspicuous fossil, it becomes one of the best guides for the determina- 

 tion of any member of the Carboniferous limestone series below the Coal formation. 



The illustrations given are but feeble representations of the beautiful and magnifi- 

 cent masses of this coral which occur in Southern Iowa and the neighboring State 

 of Missouri. 



Fig. 5 a. View of the calyces of a small group, showing the varying dimensions. 



Fig. 5 b. Vertical section of a portion of the mass, showing the columnar structure 

 where the cells are closely compressed, the elevated columella, etc. 



Geological position and localities. In the St. Loui? limestone : Mount- 

 Pleasant, and numerous localities in the valley of the Desmoines, Iowa ; 

 St. Francisville, and other places in Missouri ; Warsaw, Johnson's landing, 

 Milan, Alton, Prairie du Rocher, and other places in Illinois ; Elliottsville, 

 Indiana ; and numerous localities in Kentucky v Tennessee and Alabama. 



Lit host rot ion proliferum ( n. s.). 



PLATE XXIV. FIG. 6 a, b, c. 



CORAL dendroid, simple or in tufts, cylindrical or obconic, 

 proliferous. Calyx often profound, monticuliform, the colu- 

 mella often extremely salient ; exterior portion having the 

 celluliferous structure well developed. Rays strong, varying 

 from twenty to thirty or more in each calyx. 



The continuity of the exterior growth is often abruptly interrupted by the mode 

 of increase; the germs growing from the cup on one, two or more sides, while the 

 central or original germ is often much contracted to give room for the bases of the 

 lateral ones* which thus go on increasing till large groups are formed. 



The mode of growth of this coral is so different from that of the L. basalti forme, 

 that I cannot suppose it to be a variety of that species, which indeed does often occur 

 in separate cylindrical individuals or in groups of several together; but in no instance 

 have I observed the mode of growth shown in fig. 2 a. 



The central columella is not well shown in the figure, the section not reaching the 

 centre. In weathered specimens this feature is often very well shown, both in its 

 longitudinal extension and its narrow pointed elevation in the bottom of the calyx 



Fig. 6 a. A small group, showing the central cup, with the branches arising from 

 proliferous budding. 



Fig. 6 b. A longitudinal section, which is a little on one side of the centre. 

 Fig. 6 c. Transverse section enlarged. 



Geological position and localities. In the St. Louis limestone : Johnson's 

 landing and Milan, Illinois. 



