PALAEONTOLOGY. 55 



greatest abundance. The represented specimens are from that 

 locality. 



Plate XXII. — Fig. i represents two silicified branches with larger 

 tubes. Fig. 2 is a branch of smaller tube size. 



CLADOPORA IMBRICATA, N. Sp. 



Cylindrical ramified stems, attaining a diameter of two centime- 

 ters, attached by a massive basal expansion. Tubes opening very 

 obliquely to the surface, with narrow, transversely compressed ori- 

 fices, joining under rhomboidal outlines. The sharp subarcuate 

 lips forming the exterior margin of the orifices are closely appressed 

 to the body of the stems, and arranged in an imbricating order like 

 the scales of a fish. 



Transverse diameter of orifices two millimeters by a width of only 

 half a millimeter across the centre of the lanceolate mouths. Inter- 

 nally the tube cavity becomes nearly circular and much narrower, 

 not over half a millimeter in diameter. Pores distant. Dia- 

 phragms have not been observed. Some specimens found in the 

 drift of Michigan seem to belong to this species, which is not un- 

 common in the Helderberg limestones at the Falls of the Ohio. 



On Plate XXII., lower row, the two outer stems on the right- 

 hand side are figures of silicified specimens found at the Falls of 

 the Ohio. 



The next two species described, found in the Helderberg lime- 

 stones at the Falls of the Ohio, have not been recognized in the stra- 

 ta of Michigan, but in order to give the description of this tribe of 

 corals more completeness, I have allowed myself, in behalf of sci- 

 ence, to transgress a step beyond the prescribed limits. It is very 

 probable, however, that future collectors will find these forms in 

 Michigan. 



'is*^ 



CLADOPORA ASPERA, N. Sp. 



Cylindrical stems, from one to two centimeters in thickness, grow- 

 ing in horizontally spreading, reticulated ramifications, which are at- 

 tached by a massive basal expansion. The tubes composing the 

 basal part are prostrate, diverging toward the circumference of the 

 disk ; the orifices are compressed, fissure-like, covered by a scaly, fiat 



