BRYOZOA. 301 



Hemlphragma tenuimurale.] 



are wanting in the specimens collected by me at Ottawa and in the Minnesota form, 

 but smooth spots, consisting of clusters of mesopores, are present instead, and in 

 the immediate vicinity of the spots the zocecial apertures are larger than midway 

 between them. It is possible that Mr. Foord was mistaken in crediting the species 

 with monticules, since these spots, being more solid than the rest of the zoarium, 

 are likely to withstand weathering better and thus to appear gradually as elevated 

 points. 



Formation and locality. — In Minnesota the species is ratlier rare and restricted to the upper part 

 of the Galena shales at Kenyon, Berne and Mantorville. The same horizon contains Fusispira ventricosa 

 Hall, Orthis germana W. and S., Pachydictya pumila, Homotrypa similis, Monotrypa (9 Chcetetes) cumulata, 

 and other highly characteristic fossils. 



Mus. Beg. No. 6002. 



HeMIPHKAGMA tenuimurale, 11. sp. 

 PLATE XXIV, FIGS 20-23. 



In its growth and general aspect this species is precisely like H. irrasum. Under 

 a hand lens, however, they are immediately distinguished by the much thinner walls, 

 fewer mesopores, and seeming total absence of acanthopores in the present species. 

 In H. irrasum the zocecial apertures also are always of rounded form, in H. tenuimurale 

 angular. These differences, as may be seen from figs. 5 to 8 and 20 to 22 of plate 

 XXIV, are no less obvious when we compare the internal characters of the two 

 species. It is true, perhaps, that we may occasionally see faint evidence of very 

 small acanthopores at the angles of junction in tangential sections, yet they are too 

 indistinct and small to compare with the acanthopores of H. irrasum. In tangential 

 sections the species is much more like H. imperfectum {Batostoma imperfectum Ulrioh) 

 of the Hudson river group of Illinois and Wisconsin. But that species grows to a 

 much greater size and has rather conspicuous clusters of mesopores. II. ottawense, 

 besides being much larger and having more abundant semi-diaphragms, differs in 

 the same manner as K irrasum. 



Formation and locality.— lHot uncommon in the Galena shales at various localities in Goodhue 

 county, Minnesota. 



Mus. Beg. Nos. 8032, 8042, 8052. 



Genus . STROM ATOTRTPA, n. gen. 



Zoarium consisting of one or several superimposed thin layers growing upon 



foreign bodies. Zocecial tubes short, with few diaphragms, the proximal end 



scarcely prostrate, oval in cross-section; walls thin, containing periodically con- 



t icted bead-like tubuli (? modified acanthopores), one or more to each zooecium, 



