BEYOZOA. 243 



Homotrypa callosa.] 



to sixteen of the latter in 1 mm. The most peculiar feature of the species, perhaps, 

 is the solid filling of the cystiphragms near the surface. This is, however, a pecu- 

 liarity that is not shown to advantage except in sections of old examples. 



Foord's figures of this species (op. cit.) are not entirely satisfactory, though suffi- 

 ciently so. to make the identity of the Minnesota examples referred to it a matter of 

 high probability. Still, in making the identification I relied chiefly upon the char- 

 acters of a Canadian example kindly furnished me by the author of the species. 



The obliquity of the zooecial apertures, and the substellate surface spots will 

 serve to distinguish the species from associated forms, while its peculiar internal 

 structure separates it from all others known to me. The affinities of the species 

 are somewhat doubtful, but it is certainly not related very closely to H. obliqua 

 Ulrich, of the Cincinnati group. 



Formation and locality. The types are from the Trenton limestone at Ottawa, Canada. In Minne- 

 sota the species is an abundant fossil in the Galena shales, in the upper beds especially, at several local- 

 ities in Goodhue couuty, and at St. Paul, Minnesota. 



Mus. Reg. Nos. 7636, 8021, 8043, 8058. 



HOMOTRYPA CALLOSA, n. sp. 



PLATE XX, FIGS. 15-21. 



Zoarium irregularly ramose, less than 80 mm. high ; branches generally some- 

 what compressed, 6 to 12 mm. wide, 5 to 10 mm. thick. Surface with moderately 

 distinct clusters of large cells, sometimes raised into low monticules. Zocecial aper- 

 tures subangular, nearly or quite direct, enclosed by rather thick, ridge-shaped walls ; 

 thirteen or fourteen in 3 mm. Mesopores wanting. Acanthopores small, inconspic- 

 uous superficially. 



Internal characters: In tangential sections the most striking features are (1) the 

 thickness and minute structure of the walls (see figs. 16 and 21) and (2) the com- 

 parative straightness of the inner edge of the cystiphragms. In the Minnesota 

 specimens the latter seem to project a little farther across the zooecial cavity, while 

 the walls are uniformly a little heavier and the zooacia sometimes a trifle larger 

 than in the Kentucky form. 



In vertical sections the tubes bend outward gradually, and are tabulated through- 

 out, remotely and irregularly in the axial region, where only diaphragms occur, and 

 more crowded, also consisting chiefly of cystiphragms, in the peripheral region. On 

 plate XX, fig. 19 shows the character of the tubes near the center of the branch, 

 while figs. 17 and 18 illustrate their usual appearance in the outer fourth of the 

 diameter. In other parts of the same sections the short diaphragms crossing the 



