PAL^ONTOLOG V. 



39 



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. 



FAVOSITES DIGITATUS, N. Sp. 



Cespitose masses of subparallel anastomosing stems of the thick- 

 ness of a finger, or single stems with more straddling branches. 

 Tube walls stout, joining under polygonal outlines, lined by a 

 cycle of vertical rows of horizontal squamae, usually fewer in num- 

 ber than the normal twelve. Diaphragms sometimes regular, fre- 

 quently incomplete, replaced by the lateral squamae. Pores large. 

 Tubes in different specimens variable, from one to one and a half 

 millimeter in diameter. The polygonal form of the orifices and the 

 generally well-developed squamae within the tube channels render 

 this form at once recognizable from other branching forms of 

 Favosites, which have their orifices always more rounded, nearly 

 circular. 



It occurs in large clustered masses in the black, shaly lime- 

 stones of the Hamilton group, on the shore of Lake Huron, from 

 Thunder Bay Island, northward ; similar masses are inclosed within 

 the limestones of Little Traverse Bay, in beds of various horizons, 

 and preserved in calcified condition. On Thunder Bay River it is 

 found in silicified condition in the lower beds near Trowbridge's 

 mills ; in the drift of the Lower Peninsula, also, silicified specimens 

 associated with other characteristic Hamilton fossils can often be 

 picked up. 



On Plate XV., the six right-hand figures of the lower tier are 

 silicified specimens, of various tube size. The two outer figures 

 and the lower central branch are from the drift of Ann Arbor ; 

 the other three branches are from the north fork of Thunder Bay 

 River ; the lower small branch has considerably thickened tube 

 walls, forming within the polygonal, truncate, disciform tube ends 

 a central proboscis-like prolongation. The cespitose specimens 

 from the dark limestones, from the shore of Lake Huron and from 

 Little Traverse Bay, can not be successfully represented by photog- 

 raphy on account of their sombre color. 



