54 LOWER PENINSULA. 



stems subreniform shallow pits, impressed into a massive common 

 wall substance, composing broad interstitial spaces. The actual tube 

 opening, commencing at the bottom of these pits, is narrow, fissure- 

 like, and margined by a small lip which does not project above the pit. 

 In the ends of the branches the tube walls are less thickened, and the 

 orifices not surrounded by pits, subcircular, margined by a moder- 

 ately projecting convex lip. These terminal parts of the ramifica- 

 tions resemble the specimens figured as Clad, labiosa. The three 

 right-hand branchlets and future collections may demonstrate the 

 three last-described species to be only modifications of one ; but 

 for the present this direct affinity between them is not proved, where- 

 fore I point them out as specifically distinct. Found associated 

 with the other forms in the drift of the Lower Peninsula. 



Plate XXI., Lower tier. — The two larger specimens were found 

 in the drift of Ann Arbor, in a porous cherty rock, originating from 

 decomposition of a siliceous limestone, of which sometimes an 

 unaltered nucleus forms the centre of the boulders. The specimen 

 in the centre below the two figures represents a variety of Clado- 

 pora labiosa. 



CLADOPORA PULCHRA, N. Sp. 



Small cylindrical stems, from three to five millimeters in thick- 

 ness, growing in reticulated ramifications, composed of thick-walled 

 conical tubules, diverging in a curve from an imaginary longitudi- 

 nal axis, opening almost at a rectangle to the surface, with circular 

 orifices separated by interstitial walls wider than a tube diameter. 

 The end of each tube either projects as a small monticulose protu- 

 berance above the general surface, and is defined from the adjoining 

 tubes by delicate linear furrows circumscribing polygons, or the 

 lower half only of each tube wall projects under the form of a low 

 semicircular lip. In other specimens the single ends of the tubes 

 do not project, and are not defined in their circumference, their 

 orifices opening on the massive surface as simple circular perfora- 

 tions, surrounded at the outside by a shallow depressed area. Tube 

 diameter at the orifices one third to one half millimeter, near the 

 centre of the stems much narrower. Lateral pores numerous, in un- 

 equally dispersed position. Diaphragms sparingly developed. On 

 the casts of the tubes which frequently occur in weathered drift 



