298 THE PALEONTOLOGY OF MINNESOTA. 



[Batostotna? decipiens. 



BATOSTOMA? DECIPIENS, n. sp. 



PLATE XXVII, FIGS. 16-19. 



Zoarium ramose, branches smooth, 5 to 12 mm. in diameter. Zooecia with 

 moderately thick walls; apertures polygonal, subequal, about eleven in 3 mm. 

 When in a good state of preservation the walls are sharply ridge-shaped, appearing 

 thinner than usual. Clusters of large cells scarcely distinguishable. Mesopores 

 very few, acanthopores not observed at the surface. 



Internal characters: Vertical sections show that in the axial region the proximal 

 end of the tubes is crossed by four to six diaphragms, 0.2 mm. or less apart. Above 

 these the distance between them is from two to four times as great until the tubes 

 are about to turn into the well defined peripheral region, when their number is 

 greatly increased. In the outer part of the tubes, where the diaphragms also 

 exhibit a tendency to coalesce, the number varies in different sections from seven 

 to twelve in 0.5 mm. 



In tangential sections the walls are thick, though some difference in this respect 



is noticeable in the ten sets of sections prepared. This is owing to the varying 



* 



thickness of the internal concentrically laminated deposit. The divisional line 

 between adjoining tubes is sharply marked, and sometimes contains a small, 

 acanthopore-like dot midway or thereabout between the angles of junction. The 

 mesopores, which are scattered very sparingly among the zooecia, and sometimes 

 gathered into clusters of three or four, look very much as though they might be 

 merely young or perhaps aborted zooecia, differing from them, so far as can be seen 

 in these sections, solely in the matter of size. 



The systematic position of this species cannot be determined finally until we 

 know more of the Chazy Trepostomata. Without that knowledge its affinities appear 

 to lie as closely with B. winchelli on the one hand as with Callopora angularis on the 

 other. I thought much of classing the species with Callopora, but at last concluded 

 that the occasional presence of acanthopores and greater thickness of the walls 

 would not now admit of such an arrangement. Callopora angularis, which of all the 

 associated species is probably the most like B. ? decipiens, has smaller branches and 

 thinner zocecial walls. 



Formation and locality. Rather rare in the lower and middle third of the Trenton shales at Min- 

 neapolis, Minnesota. 



