PALAEONTOLOGY. 



2>1 



the large circular tubes are in great contrast with the smaller sub- 

 angular ones. The right-hand lower figures are single branches from 

 the usual variety occurring in the corniferous limestone of Michigan, 

 Canada, New York, and in the Western States. The specimens 

 selected are also from the Falls of the Ohio. 



FAVOSITES INTERTEXTUS, N. Spec. 



Irregularly reticulated masses of cylindrical or compressed 

 elliptical stems, from one to two centimeters in thickness. Tubes 

 quite unequal, stout-walled, the larger ones circular, the smaller 

 subangular, filling the interstitial space between the larger tubes. 

 Size of the larger tubes not much over half a millimeter. In the 

 centre of the stems the tube channels are regularly formed, with 

 moderately thick walls, and intersected by complete or incom- 

 plete squamiform diaphragms, and connected by distant pores. 

 In the peripheral portions of the stems, the tube channels, by 

 habitual thickening of the walls, have shrunk to filiform thin- 

 ness, while the lateral pores have become more profusely de- 

 veloped and equal in width to the shrunken tube channels. Here- 

 by a network of anastomosing ducts is formed, which can not 

 be properly observed in fully-preserved specimens ; in the drift, 

 however, weathered specimens frequently occur in which the 

 casts only of these reticulated ducts are preserved in silicified con- 

 dition, the wall substance having all decayed. No one would 

 likely recognize in these networks the casts of a Favosites if parts 

 of the fully-preserved coral were not found in immediate contiguity 

 to such networks. The contracted tube channels usually expand 

 again to their normal diameter in close proximity to the surface. 

 Found in the upper limestones of Mackinac and in the drift of the 

 Lower Peninsula. 



Plate XV. — Fig. i represents reticulated tube casts with the central 

 portions of the stems formed by normally shaped tube channels. 

 The object is too minute in the specimen. On Plate X., Fig. 4, 

 similar casts of somewhat coarser stems are represented. On Plate 

 XV. the upper left-hand figure is a palmate branch found in the 

 drift of Ann Arbor ; some specimens have much stouter stems, 

 while others are only of the thickness of a lead-pencil, forming retic- 

 ulated clusters. 



