310 THE PALEONTOLOGY OF MINNESOTA. 



[Var. ornata. 



outer ones of which are much thicker and separated by shorter intervals than the 

 inner pair. This gradual thickening of the diaphragms is more decided in the 

 branches than in the basal expansion, part of a vertical section of which is rep- 

 resented in fig. 40. The walls of the mesopores where two or more occupy an inter- 

 space are strongly zigzag, in some instances appearing not unlike vesicular tissue. 

 In tangential sections the zooecial walls may be thin and occasionally even inflected 

 by the acanthopores (fig. 37), but as a rule they are ring-like, as in figs. 38 and 39, and 

 generally completely separated from each other by a series of unequal and irregu- 

 larly shaped mesopores. The acanthopores are distinct, nearly uniform in size, 

 usually attached to the outer side of the zooecial walls, and number from one to 

 three or four to each zocecium. 



Var. ORNATA Ulrich. 



PLATE XXI, FIGS. 26, 28, 33, 34. 



Trematopora ornata ULRICH, 1886. Fourteenth Ann. Rep. Geol. Nat. Hist. Surv. Minn., p. 98. 



Increased collections have convinced me that this is merely an uncommon 

 variety of T. ? primigenia, differing from the typical form of the species, as above 

 described, in having the zooecial apertures a little more elongate and rather more 

 regularly arranged, and in having the peristomes crowned by a crowded row of 

 small papillae. Larger spines, as shown in fig. 34, are sometimes present. 



Var. SPINOSA, n. var. 



PLATE XXI, FIGS. 29, 30, 35. :\. 



Of this form, which, if it proves permanent, should be called a species, I have 

 seen only a few specimens. Though evidently mature they are a trifle smaller than 

 typical T. ? primigenia, and differ in a number of other minor points from that form. 

 But their principal peculiarity, and the only one that in the present state of our 

 knowedge deserves mention, is the presence of a considerable number of strong 

 spines in the interspaces. A few smaller acanthopores are scattered among the 

 larger ones, but unless searched for they are likely to be overlooked. 



The large basal expansion, small branches, rounded zooecial apertures and 

 depressed interspaces are features that serve to distinguish this species and varieties 

 at once from all associated ramose Bryozoa. 



Formation and locality. The typical form is an abundant fossil in the middle third of the Trenton 

 shales at St. Paul and Minneapolis, while it is not uncommon in the same beds at other localities in the 

 State, notably near Fountain and Preston in Fillmore county. The two varieties are rare and associated 

 with the typical form at St. Paul and vicinity. 



Mus. Reg. Nos. 6010, 6011, 7654, 7661. 



