264 THE PALEONTOLOGY OF MINNESOTA. 



[Bythopora alclcornis. 



The species is closely related to B. ardipora Nicholson, sp., of the Cincinnati 

 rocks, but the zocEcial apertures are narrower and more produced anteriorly than in 

 that species. 



Formation and locality. — Fragments of this species are common in the middle third of the Trenton 

 shales at St. Paul and Minneapolis, Minnesota. Good specimens, however, are rare. 



Mus. Reg. Nos. 6012, 6013. 



Bythopora aloicornis, n. sp. 



PLATE XXVI, FIGS. 7-9. 



In this species the zoarium divides at shorter intervals than in any other of the 

 genus known, the distance between the branches varying between the extremes of 1.5 

 to 6.0 mm. Compared with B. herricki, we find that the average size of the branches 

 is a little less,, that they bifurcate at shorter intervals, that the zooecial apertures are 

 arranged less regularly and on the whole less compactly, the direction of the rows 

 being interrupted and changed by meeting with spots, 2 or 3 mm. apart, in which 

 the interspaces between the apertures are much wider than elsewhere. These sub- 

 solid spots distinguish the species from all the others as well, excepting an unde- 

 scribed larger form occurring in the upper beds of the Hudson River group at 

 Waynesville, Ohio, in which they are of greater extent and constitute a very obvious 

 superficial character. 



Formation and locality.— Upper third of the Trenton shales, associated with Phylloporina corticosa 

 and Prasopora eonoidea, near Cannon Falls, Minnesota. 



Genus ERIDOTRTPA, n. gen. 



Batostomella (part.) Uleich, 1890. 111. Geol. Sur., vol. viii, pp. 375, 432. 



Zoaria ramose, branches slender. Zooecia more or less oblique, with thick walls, 

 the tubes intersected by diaphragms only. The latter may be wanting in the axial 

 region, are in most cases absent for a short distance within the apertural edge, but 

 always present and closest together in the turn from the axial into the narrow 

 peripheral region. Mesopores with close-set diaphragms, varying in number, some- 

 times abundant, at other times very few. Acanthopores small, never numerous, 

 sometimes wanting. 



Type : Eridotrypa mutabilis, n. sp. 



This genus became necessary partly through the restriction of Batostomella to 

 its Carboniferous types, and partly for the accommodation of a number of species 

 that could not be disposed of satisfactorily under any of the existing genera.* The 



*It is unfortunate that both Hall's recently proposed TrematelU (Pal. N. Y., vol. vl, p. xly, 1887) and my BatostomeUa (1882) 

 should have been founded upon practically the same type of structure. In both cases species are Included doubtfully that 

 are now to go under Enaotrypa. ; ' 



