50 LOWER PENINSULA, 



velopment of a character typical for the whole family to which it 

 belongs. 



Found in the upper Helderberg limestones of Michigan, New 

 York, Canada, and in the Western States ; also common in the drift 

 deposits of Michigan. 



Plate XX. — Fig. i represents several fragments of branches with 

 the larger tubes. Orifices somewhat variable in different branches. 

 Fig. 2 is the variety with smaller tubes, corresponding in all partic- 

 ulars with the larger tubed form. All the specimens figured are 

 selected from the Falls of the Ohio, as being better preserved than 

 those from any other locality. 



CLADOPORA ROEMERI, Billings, i 

 Alveolites Roemeri, Billings. 



Cylindrical or compressed branching stems of about five millime- 

 ters diameter. Orifices comparatively large, oblique to the surface, 

 and joining with their expanded margins in an indefined interstitial 

 surface, or under subangular, obtusely crested outlines, inclosing 

 shallow, obliquely funnel-shaped pits, the outer margins of which 

 project as arched lips ; the inner walls of the pits spread insensibly, 

 merging into the lips of the adjoining pits. External diameter of 

 orifices about one millimeter; interior tube channel one third of a 

 millimeter. The orifices are frequently closed by opercula situated 

 below the external margins. Diaphragms in most of the specimens 

 sparingly developed. Pores large and irregularly disposed. 



Occurs in the Hamilton strata of Widder, Canada West, in cal- 

 cified condition. Silicified specimens are found in the corniferous 

 limestone and in boulders of that formation, mingled with the 

 drift of the Southern Peninsula. 



Plate XX. — Fig. 3 represents specimens from the typical locality 

 of Widder, Canada West. 



CLADOPORA ALPENENSIS, N. Sp. 



Branching cylindrical stems, from five to ten millimeters in 

 diameter. Orifices slightly oblique, dilated, joining under [linear 

 polygonal outlines on an even, narrow, interstitial surface ; external 



