ORDOVICIAN FOSSILS 



47 



One of the most abundant forms of twig-like bryozoans is the genus Hallopora . 

 Some forms possess monticules but one, H. oneilli , has none. H. ramosa (fig. 53) 

 has numerous distinct monticules on colonies about l/4 inch in diameter; in H. ru- 

 gosa (fig. 54) the monticules more or less fuse into sharp ridges; both of these 

 species are found in the McMillan formation. 





Fig. 52 



Fig. 53 



Fig. 54 



Fig. 55 



Fig. 56 



All of the following species are twig-like but without monticules. Hallopora oneilli (fig. 55) 

 has small (diameter about l/l6 inch) branches with coarse tubes. Rhombotrypa quadrata has 

 branches 1/4 inch or more in diameter which are of approximately the same size throughout; 

 the tubes are almost square in cross-section; it is found in the Richmond. Batostoma jamesi 

 (fig. 56) is like Rhombotrypa quadrata but the tubes are almost round in cross section and the 

 branches thicken irregularly at intervals; it occurs in the Eden. Bythopora gracilis has such 

 small tubes that the surface of the branches (diameter about 3/16 inch) appears smooth; it is 

 found in the McMillan formation. Bythopora meeki is larger (diameter of branches about 5/16 

 inch) than B. gracilis and has different internal characters; it is found throughout the Richmond. 



Escharopora falciformis has unmistakable characteristics that separate it from all others. 

 It is twig-like but not branching, the colony is flattened and pointed at one end. The tube open- 

 ings are arranged in diagonal rows; it is confined to the Fairview formation. 



The following species have twig-like, branching colonies but they are flattened and expanded 

 so that the larger end of the colony often looks more like a fan or leaf than a twig. They have 

 no monticules. Dekayia as per a of the Fairview formation is distinguished from Chiloporella 

 flabellata of the McMillan by internal characters; externally, they look alike except to the most 

 practiced eye. 



Homotrypa dawsoni of the Waynesville has twig-like, flat, expanded branches and monti- 

 cules like Monticulipora mammulata . H. flabellaris has no monticules; its twig-like, flattened, 

 wide branches maybe 3/4 inch Wide or more; it is found in the Maysville and Richmond. H. obliqua 

 is twig-like to fan-shaped, has no monticules but patches (called maculae) in which the tubes 

 are larger than on the remainder of the surface; it is found in the Fairview. 



The following species are sheet-like, occurring in crusts on other objects or rising in fan- 

 like colonies from the original sheet. Constellaria florida (fig. 57) of the Fairview has numer- 

 ous star-shaped monticules which are characteristic of the genus; C. polystomella (entire 

 Richmond) differs from C. florida by its internal characters. Monticulipora mammulata grows 

 in delicate fan-shaped colonies; its surface has numerous, sharp monticules; it is found in the 

 Fairview. Monticulipora molesta of the McMillan formation is very similar to M. mammulata 

 but differs from it in being coarser and larger. Heterotrypa frondosa of the" Fairview has a 

 fan -shaped colony with low, numerous, widely spaced monticules. 



The following three genera have no monticules. Aspidopora newberryi has 

 disk-shaped colonies of irregular outline; it is found in the Eden. Homotrypella 

 hospitalis of the entire Richmond is also disk-like but its colonies are hemispheri- 

 cal. Peronopora vera has fan-shaped colonies with tubes on both surfaces; it is 

 found in the entire Cincinnatian. 



Fig. 57 



