126 



BULLETIN 77, UNITED STATES NATIONAL MUSEUM. 



made up of similarly modified zooecia and broad interspaces. In 

 all cases, the elevated lines traversing the interspaces are minutely 

 papillose. Views of the internal structure are given in figure 50. 



Occurrence. — Eichwald mentions two localities for his species, first, 

 the ''calcaire a Orthoceratites'' at Reval, and, second, the dolomite 

 Pliyckholm-Borkholm formation] at Borkholm. The nmnerous 

 examples coming from the Wassalem beds (D3) at Uxnorm, in the 

 vicinity of Reval, identical with his figured specimen, cause me to 

 beheve that the latter was derived from the same place. Eichwald's 

 Borkliolm specimens probably belong to the species next described 

 as Graytodictya obligua. The American occurrences are (1) in the 

 Clitambonites bed of the lower Trenton limestone, near Kenyon, 

 I^iinnesota, and (2) in the lowest Trenton or late Black Kiver limes- 

 tone, along the Escanaba River, IVIichigan, below the falls. 



Plesioty pes. —Csit. No. 57216, U.S.N.M. 



Specimens and thin sections from the Wassalem beds at Uxnorm, 

 Esthonia, are in the collections of the British Museum. 



GRAITODICTYA OBLIQUA, new species. 

 Plate 8, fig. 4; text fig. 51. 



Compared with other cribrose species, this new form differs so 

 decidedly in zooecial structure that it need be discriminated only 

 from the abundant Graptodictya proava (Eichwald), of the Wassalem 

 beds. Careful comparison shows the following differences: First, 



Qk 



Pi ^ I "" 



rm 



Fig. 51.— Geaptodictta obliqija. a, the type-specimen, natural size, showing the striated basal 

 portion; 6, tangential section, x20, exhtbiting the wide, interzocecial spaces; c, vertical 

 section, X20, with the interzocecial spaces filled by iaminated tissue. Lower part of Lyck- 

 HOLM -umestone (Fl), Kertel, island of Dago, Esthonia. 



the zoarium of G. ohliqua is much coarser, its fenestrules being twice 

 the size of those in G. proava. Its zooecia also are larger, with four 

 in 2 mm., and are directed obliquely to the growing edge; the orna- 

 mentation of the surface is likewise coarser. Altogether G. obligua 



