42 LOWER PENINSULA. 



of Ann Arbor. Fig. 2 is found at Drummond's Island. The latter 

 specimen exhibits the longitudinal rows of spinules very distinctly, 

 but the object is too small to be properly seen in the not magni- 

 fied figure. 



ALVEOLITES SQUAMOSUS, Billings. 



Convex masses of irregular growth, covered by an epithecal crust 

 on the partially free, centrally attached under side, or sometimes 

 incrusting other marine bodies. Tubes in the broader, transverse 

 direction from one half to one millimeter in diameter, and in the 

 other direction quite variable, in accordance with the degree of 

 depression of the tubes, which are convex on the upper side and 

 concave on the lower. Orifices very oblique, with a sharp lip on 

 the outer margin. Tube channels longitudinally crested by twelve 

 well-developed rows of spinules, of which generally some are larger 

 than the others. Diaphragms not very close, and irregularly 

 oblique. Pores large, marginal, but not causing a pouch-like dilata- 

 tion of the tubes as in the Niagara species. 



Found in the upper Helderberg limestones of Michigan, and in 

 the drift ; common also in the Helderberg limestones of Canada, 

 New York, Ohio, Louisville, etc. 



On Plate XVI., Fig. 3 is a silicified specimen found in the drift, 

 giving a surface view ; Fig. 4, likewise found in the drift, is com- 

 posed of casts of the tubes. They are delicately punctured by im- 

 pressions of the longitudinal rows of spinules. They exhibit the 

 laterally situated pores and the distant, irregular diaphragms. The 

 figures are of natural size. 



. ALVEOLITES VALLORUM, Meek. 



(Paleontology of Mackenzie River.) 



Specimens resembling the forms described by Mr. Meek, from 

 Mackenzie River, are frequently found among the drift pebbles of 

 Lake Superior. In some of them the tube walls are preserved ; 

 in others only the casts of the tube channels, which have the form 

 of narrow, flat bands, connected with each other by short marginal 

 bridges, representing the pore channels. The bands are longitudi- 

 nally striate by fine, punctiform impressions, and transversely inter- 

 sected by numerous closely approximated diaphragms. The width 



