274 THE PALEONTOLOGY OF MINNESOTA. ^ , . 



[Dekayia. 



Genus DEKATIA Edwards and Haime. 



Dekayia, Edwabds and Haime, 1851, Mon. Pol. Foss. Terr. Pal., p. 277 ; Nicholson, 1879, Pal. 



Tab" Corals, p. 291; 1881, "Genus Monticulipora," p. 98; Uleich, 

 1882, Jour. Gin. See. Nat. Hist. vol. v, p. 155, and vol. vi, p. 148 ; also 

 1890, Geol. Sur. 111., vol. vili, pp. 371 and 415. 



Zoaria irregularly ramose; branches subcylindrTcal or compressed, growing 

 from a broad base. Zooecia polygonal, walls thin. Mesopores wanting or very few, 

 when present restricted to the maculge. Acanthopores originating in the outer part 

 of the axial region, in most cases rather widely separated, often of large size ; in 

 other cases small, and in one instance equalling the zooecia in number. Diaphragms 

 straight, in most cases remote, sometimes from one-half to one tube diameter dis- 

 tant in the peripheral region; wanting usually in the axial region. A thin calca- 

 reous pellicle often drawn over the zooecial apertures. 



Type : D. aspera *Ed. and H., Hudson River group. 



For remarks see under Dehayella, p. 269. For more detailed observations and 

 full descriptions of all the known Lower Silurian species, the reader is referred to 

 my "American Paleozoic Bryozoa."* Beside the following, another as yet unde- 

 scribed species of Dekayia, with fewer diaphragms, thinner walls and smaller acan- 

 thopores than D. trentonensis, occurs in Minnesota. It is rather rare, and so far 

 known only from the Galena shales of Goodhue county. 



Dekayia trentonensis Ulrich. 



(Not Figured.) 

 Dekayia trentonensis Uleich, 1882. Jour. Gin. Soc. Nat. Hist., vol. vi, p. 151. 



Zoarium dendroid, branches compressed, dividing frequently and rather irregu- 

 larly, 4 to 10 mm. in width. Entire hight of zoarium probably not exceeding 8 or 9 

 cm. Surface even, or with low rounded monticules, 2.5 mm. apart ; the latter occu- 

 pied by clusters of cells a little larger than those in the intermediate spaces, and 

 occasionally have a few mesopores at their summits. Zooecia with comparatively 

 thick walls, their apertures subangular, about fourteen in 3 mm. Acanthopores 

 rather large, moderately prominent at the surface where six or seven are to be 

 counted in 3 mm. 



Internal characters: In the axial region of vertical sections the tubes have very 

 thin and slightly flexuous walls,, and are crossed by diaphragms from two to four 

 times their diameter distant from each other. Bending into the peripheral region 



*Jour. Gin. Soo. Nat. Hist., vol. vl, pp. 84 and 148-155. 



