30 LOWER PENINSULA. 



or warped by marginal depressions, more rarely of broken, angu- 

 lar surface through complication with the lateral squamae, as 

 in Favosites hemisphericus. Pores comparatively small, surrounded 

 by an elevated rim, in a single or double row on each side, never 

 very much crowded. Grows in discoid, subundose expansions, 

 with a delicately wrinkled epithecal crust on the lower side, having 

 a narrow conical centre serving as point of attachment. Found in 

 the upper limestones of Mackinac Island, and of frequent occur- 

 rence in the drift ; likewise common in the corniferous limestone 

 of Canada, New York, Indiana, and Kentucky. From the forms 

 with deeply furrowed, crenulated orifices, and with irregular, com- 

 pound diaphragms, insensible transitions exist to specimens with 

 almost smooth, faintly furrowed tubes and with simple, straight 

 diaphragms. In the size of the tubes also a considerable variation 

 exists in different specimens. 



Plate VIII. — Fig. i is a silicified specimen from Caledonia, N. Y., 

 with beautifully crenulated orifices, exhibiting the longitudinal 

 furrows and intermediate squamose projections. Fig. 2 is a silici- 

 fied specimen found in the drift of Ann Arbor, seen from the 

 lower side. Fig. 3 is a specimen from Port Colborne, showing 

 the diaphragms with marginal depressions, and the general sur- 

 face aspect. 



FAVOSITES CANADENSIS. 



[Vide *' Silliman's Journal," November, 1862.) 



FiSTULiPORA Canadensis, BilHngs. 



Undose expansions, with an epithecal crust on the lower side, 

 sometimes of digitato-ramose or reticulated growth, with orifices 

 on all sides of the stems. Tubes of two strikingly different sizes. 

 The larger ones, about one millimeter wide, are circular, dispersed 

 at subregular intervals between a mass of smaller subangular tubes 

 about one third the size of the circular tubes. The specimens have 

 a great resemblance to Heliolitesporosus, or, as Mr. Billings thinks, 

 to Fistulipora. The radiated structure of the tubes and the devel- 



