66 LOWER PENINSULA. 



Goldfuss,' in external structure, but more minute, the diameter of 

 the tubes being only one third to one half millimeter. Interstitial 

 surface smooth, neither rugose nor granulose. Found in the upper 

 strata of the Hamilton group at Partridge Point, and in the lower 

 beds on Thunder Bay River, at Broadwcll's mills. 



Plate XXIV., — Fig. i. The lower piece represents a reticulated 

 expansion from Partridge Point, Thunder Bay. On the same plate. 

 Fig. 4, the upper row of stems are magnified fragments (two 

 diameters) of the same kind, found at Broadwell's mills, on Thun- 

 der Bay River. 



THECIA, Milne-Edwards. 



Massive or rarely dendroid polyparia with the general structure of 

 Favosites. Tube walls very thick, forming, by their junction under 

 defined polygonal outlines, solid interstitial spaces as wide or even 

 wider than a tube diameter ; sometimes, however, the walls do not 

 exceed in thickness those of an ordinary Favosites, and the dilated 

 tube margins join with edged polygonal margins. Tubes radiated by 

 twelve spinulose, longitudinal crests almost extending to the centre, 

 with intermediate, narrow, linear furrows. The internal crests of the 

 orifices are sometimes prolongated externally, and extend as low 

 radial rugae across the surface of the interstitial spaces from one 

 tube into the other ; or the interstices, if large, are irregularly granu- 

 lose on the surface. Transverse diaphragms well developed, flat or 

 ■convex, projecting within the orifices as a central boss and covered 

 with spinules or granules like the other surface of the tube cavity. 

 Lateral pores large and abundant. Tubes frequently subject to in- 

 crassation at the expense of the lumen of the tube cavities, while 

 the pore channels retain their original diameter and become longer, 

 The external appearance of such specimens becomes thereby con- 

 siderably altered, and in silicified specimens, in which the silex is 

 deposited in the peculiar concentric, annular dots so often noticed, 

 the structure becomes so much obscured that it would be impos- 

 sible to recognize their true nature if it were not that other, better 

 preserved specimens, only partially altered in this way, can be 

 found amongst them. The genus Protaraea of Milne-Edwards, 



