52 LOWER PENINSULA. 



margins not projecting as a lip, excepting a small nodular projec- 

 tion in the centre of the outer margin, which gives the transversely- 

 widened, elliptical mouths a faint kidney shape. The inner expanded 

 margin of the orifices is very delicately striate in radial direction. 

 Diameter of orifices externally about one millimeter ; internal tube 

 cavity about half a millimeter wide. Diaphragms rarely noticed. 

 Pores large and irregularly dispersed. 



Found in silicified condition in the upper strata of the Hamilton 

 group of Thunder Bay. 



Plate XX. — Fig. 4 represents a few of the branchlets. The linear 

 polygonal outlines of the tubes are recognizable in the figures ; the 

 striation of the marmns is too delicate to be seen on them. 



CLADOPORA LABIOSA, Billings. 



Alveolites labiosa, Billings. 



Small, branching, reticulated stems, from two to five millimeters 

 in diameter, growing from an attached, massive root portion in hori- 

 zontally spreading direction. Orifices oblique to the surface, sub- 

 circular, surrounded on the exterior side by a prominent convex 

 lip ; the interior part of the orificial tube walls spreads into an un- 

 defined, flat, interstitial surface. By wearing of the surface the lips 

 often become deeply sinuated in the centre, and then the orifices 

 are acutely triangular. In certain specimens considered to be a 

 variety of this species, the closely crowded small orifices are sur- 

 rounded by small pits impressed in the thick wall substance, and 

 open on the surface with less obliquity than in other specimens, 

 and with only a small lip developed^ on the exterior margin. The 

 size of the tubes differs somewhat in the specimens, but a more ob- 

 vious difference in appearance is caused by the variations in the 

 width of the interstitial spaces. In some specimens the orifices are 

 separated by interstices less than the diameter of a tube, while in 

 others the interstitial space is two or three times as large. In 

 adult parts of stems the intervals between the orifices are always 

 greater than they are near the terminal branchlets. The diameter 

 of tubules at the orifices is about half of one millimeter ; internally 

 the channels are narrower. Within the cavity of some tubes, on 

 the outer side of the walls, two crests can be noticed by looking into 



