170 THE PALEONTOLOGY OF MINNESOTA. 



[Escharopora . 



In 1886 I believed this species to be a close relative and, perhaps, the western 

 representative of Hall's E. recta. Since making my final investigations, with aug- 

 mented material in all stages of growth, much of it in an excellent state of preser- 

 vation, I find that the relationship is more remote than it seemed at first. Although 

 I have not had an opportunity of examining authentic examples of E. recta, Hall's 

 original figures are sufficiently diagnostic to warrant us in saying that the New 

 York species has zooecial apertures agreeing both in shape and arrangement with 

 those of E. falciformis (Nicholson) and the closely related E. acuminata ^ James). 

 The last is the form referred to {he. cit.) as occurring "in the lower beds of the 

 Cincinnati group (Utica shale ?) in Ohio." The form mentioned at the same time as 

 found in Tennessee ("Glade" limestone) greatly resembles E. acuminata, but as I 

 have not yet examined its interior structure, I cannot say that it is really the same. 

 Whatever it may turn out to be I am satisfied that it is distinct from E. suhrecta. 

 Comparing ordinary examples of the Minnesota species with any of these forms, 

 indeed with all of the known simple species of the genus, we find-that in none 

 of the latter, save ior a short distance above the pointed l)ase, are the zocecial- 

 apertures confluent longitudinally, i. e. connected by narrow channels, as is the case 

 in E. subrecta. Nor do any of them exhibit as much diflference in the size of the 

 marginal and central rows of apertures. Of unbranched species, E. subrecta is also 

 the only one known to me in which the primitive cell assumes the peculiar clavi- 

 form shape shown in figs. 25 and 26. In most of the other species, perhaps all save 

 E. angularis, the hemisepta are more pronounced. These two features alone are 

 sufficient in distinguishing thin sections of E. subrecta. Compared with the branch- 

 ing forms, we find one, and it is associated in the same beds, that agrees in many 

 respects. This is the next described E. confluens, having confluent zooecial apertures, 

 a similar difierence in the size of the marginal and central rows, and an internal 

 structure nearer that of E. subrecta than any other species. But the zpoecial 

 apertui-es are wider, a fact noticeable enough to enable one to distinguish the 

 merest fragments. There is, of course, no likelihood of confusion when complete 

 zoaria are available. 



Formation and locality.— Coraxaon In the middle third of the Trenton shales at Minneapolis and 

 other localities in the state, and Decorah, Iowa. Perhaps, also, in the lower third of the shales, but rare 

 in these and smaller than usual. A single example collected by Mr. Charles Schuchert from the "Lower 

 Blue beds " near Beloit, Wisconsin, seems to belong to this species. 



Mus. Reg. Nos. 5929, 7558 and 7597. 



