62 LOWER PENINSULA. 



they appear as impressed pits, or have at least no projecting rim. 

 Their form is either circular or elongate elliptical. Sometimes 

 they are disposed in regular longitudinal rows on the stems, but 

 are also often irregularly dispersed. The obliquity of the tube 

 mouths to the surface is variable, and in some species they open 

 almost rectangularly to it. In a part of the species the tube chan- 

 nels are longitudinally striate, as in Striatopora, but usually this 

 striation is obscure. 



DENDROPORA ORNATA, N. Sp. 



Circular stems, from one to two centimeters in diameter, with 

 dichotomous ramification. Orifices circular or oval, rising above 

 the surface by a monticulose circumvallation, or nearly even with 

 it, of unequal size and irregularly dispersed over the massive inter- 

 stitial surface of the stems, which is usually wider than a tube diam- 

 eter, with exception of the ends of the stems, where the orifices are 

 separated by comparatively narrow intermediate walls. The inter- 

 stitial surface is decorated by granules and short ridges disposed in 

 loose radial order around the circumference of the orifices. Periph- 

 eral diameter of orifices about one and a half millimeter ; within 

 they gradually contract to a diameter of not more than half a milli- 

 meter. The terminal ends of the branches have somewhat larger 

 orifices with thinner walls, greater obliquity to the surface, and are 

 surrounded by a more or less projecting lip on the exterior side, as in 

 the case of specimens of Cladopora or Striatopora, from which these 

 parts differ only by the granulated edges of the interstitial walls. 

 In polished vertical sections through calcified stems, the tubes are 

 found to be decorated with a cycle of longitudinal rows of spinules, 

 and the development of distant transverse diaphragms and of large 

 connecting pores can likewise be ascertained. Found rarely in the 

 Hamilton group of Thunder Bay, but very common in the Hamil- 

 ton strata of New York, at Darien, Eighteen-Mile Creek, Seneca 

 Lake, etc. ; at Widder, in Canada, it also sparingly occurs. 



Plate XXIII. — Fig. i represents specimens from Darien, in calci- 

 fied condition. 



Plate XXIV., Fig. 2. — Lower figure to the right is a young sili- 

 cified branchlet found at Alpena, Mich. It exhibits a scar of at- 

 tachment at the lower end. The ends of the branches are formed 



