172 



THE PALEONTOLOGY OF MINNESOTA. 



[Baoharopota. 



and Tennessee tpyes of that species was not possible before the following year, when 

 I became satified that the Minnesota specimens were really quite different, though 

 similar in their growth. In E. ramosa the zocecial apertures are set into regularly 

 hexagonal spaces, and are in no sense to be called "confluent." 



Formation and ZocaZt«2/.— Apparently restricted to the middle third of the Trenton shales, at Minne- 

 apolis, Minnesota. Fragments of a very similar, perhaps identical, species have been "observed in the 

 " Pierce" limestone at Murfreesboro, Tennessee. 



Mus. Reg. No. 8208. 



EscHAEOPOEA (?) LIMIT AEis, w. §jo. or var. 



PLATE Xm, FIGS. 12 and 13. 



Under this name I propose to arrange a form that may well be regarded as the 

 beginning of the branching section of the geniis Phcenopora, Hall. I would have 

 placed it under that genus but for the fact that I found it impossible to draw 

 a satisfactory line between it and E. confluens. Ordinarily the branches of the 

 present form are smaller and more evenly convex, their edges less sharp, and with a 

 wider non-poriferous border than in typical E. confluens; but in other specimens, 

 one in particular, the shape and general aspect of the zoarium is precisely as in the 

 most typical examples of the species. The single constant peculiarity of E. ( ?) limi- 

 taris consists in the development of an elevated rim at the ends of the zocecial 

 apertures, causing them to lose their confluent character, and to assume a definite 

 elliptical shape. At the same time the "channel" has been transformed into an 

 elongated inter-apertural pit. Frequently, instead of the single long pit, the space 

 is divided into two short o;ies, as in Phcenopora wilmingtonensis, and P. incipiens. 



The usual appearance of the surface may be imagined when I say that it is a 

 intermediate between the appearances represented in flg. 20, plate XII, and fig. 5, 

 plate XIII, on the one side, and figs. 14 and 23, plate XIII, on the other. 



FiGu 9. Etcharopora (9) limitaris Ulbich. a, small part of tangential section, x50, showing struc- 

 ture immediately beneath the point of bifurcation ; 6. another portion of same where the zoarial margins 

 are parallel. , 



