6o LOWER PENINSULA. 



STRIATOPORA CAVERNOSA, N. Sp. 



Stunted ramifications of cylindrical or compressed stems, from one 

 to two centimeters in diameter. Tubes large, in comparison with 

 the size of the stems, and very unequal through the frequent inter- 

 calation of young tubes. Orifices oblique to the surface, rounded, or 

 of irregular shape, joining with obtusely edged stout walls. They 

 form gradually dilating, spacious, deep funnels, which are longitudi- 

 nally grooved by a cycle of twelve well-marked striae. A remarkable 

 abundance of large irregularly dispersed pores perforates the tube 

 walls within the orificial funnels, and even close to their external 

 edges. Diaphragms fiat, well developed. Diameter of full-grown 

 tubes at the orificial ends from two to three millimeters ; internal 

 tube cavities one millimeter wide. Occurs in the drift of Michigan, 

 associated with corniferous limestone fossils, and is found in place 

 in the corniferous limestones of Port Colborne, Canada West ; rarely 

 also at the Falls of the Ohio. 



On Plate XXIII., Fig. 3, are small silicified fragments found in 

 the drift of Ann Arbor. 



STRIATOPORA LINN^ANA, Billings. 



Dichotomously branching stems, from a few millimeters to one 

 centimeter in diameter. Orifices moderately oblique to the sur- 

 face, joining under acute polygonal margins, which inclose funnel- 

 shaped orifices, and project on their outer margin as prominent lips. 

 Tubes very unequal in size, through the frequent intercalation of 

 young tubes. Orificial margins grooved by a cycle of twelve deep 

 furrows, and the interstitial, band-like spaces are decorated with 

 longitudinal rows of spinules, which in the narrower neck portion 

 of the tube channels project as stelliform radii. Pores large and 

 very abundant, perforating also the expanded parts of the orificial 

 walls. Diaphragms well developed in some of the specimens. 

 Diameter of the peripheral tube margins about two millimeters ; 

 of interior parts one millimeter or less. 



Occurs in the Hamilton group of Thunder Bay in silicified condi- 

 tion, and at Widder, in Canada West, in calcified form. 



