PAL.^EONTOLOG Y. 



47 



young tubes from older ones, the disposition of distant diaphragms, 

 the more rounded and dilating peripheral tube ends, bent into sub- 

 erect position — all can be studied in such casts to much better ad- 

 vantage than in the most perfectly preserved specimens. 



CLADOPORA FISHERI, Billings. 

 Synon., ALVEOLITES Fisheri, Billings. 



Palmate, laminar expansions, attached by a clumsy, massive root 

 portion to other bodies. Orifices on both sides of the leaves, open- 

 ing obliquely to the surface, with a sharp lip on the exterior side ; 

 the inner tube margin merges into a common interstitial surface, of 

 variably broader or narrower extent. The thickness of the tube 

 walls and the obliquity of the orifices vary much in different parts 

 of the specimens, and accordingly the surface characters are quite 

 changeable. On the terminal edges of the fronds the tubes 

 are thin-walled and the orifices join with sharp, crested outlines. 

 In the central and basal portions of the expansions, the walls 

 are thickened, and the oblique orifices separated by intervening 

 solid interstitial spaces, margined on the exterior side by a lip, 

 which surrounds a transversely oval, or often a nearly circular 

 mouth. Sometimes the orifices are not lipped, and form shallow, 

 undefined depressions in the massive wall substance, at the bot- 

 tom of which the narrower part of the tube channels begins. Again, 

 these superficial pits are circumscribed by polygonal, carinated out- 

 lines. A difference also exists in the upper and lower surfaces of 

 the fronds, v/hich seem to have grown in horizontally spreading 

 direction. The upper side is always marked by sharper, more pro- 

 jecting contour lines, while on the lower surface all the contours 

 are dull and rounded. 



The orifices are about one half a millimeter wide, or somewhat 

 larger, oval or kidney-shaped on the external margin ; the inner tube 

 portions are round or subangular. Pore channels are large and 

 numerous. Diaphragms frequently developed under the form of 

 superficial opercula, frequently noticed also in the inner portions of 

 the tube channels, but in specimens with very stout-walled tubes 

 rarely observed. The original specimens described by Billings were 

 found in the Hamilton group of Widder, C. W., in calcified con- 



