RRYOZOA. 269 



Dekayella.] 



in the cortical region and wanting in the axial, at other times about two tube diam- 

 eters apart in the axial and close-set in the peripheral region. They are commonly 

 horizontal, often concave, sometimes infundibular and occasionally simulate cysti- 

 phragms if they are not of that nature. Acanthopores very numerous, inflecting 

 the viscerial cavity so as to give it a petaloid appearance. 



"The extremely large size of this species, the remarkable development of acan- 

 thopores and mesopores and irregular character of the diaphragms are its leading 

 features. Some points of its structure leave me in doubt as to this being its rightful 

 position, but for the present it seems best to place it with Heterotrypa." 



Formation and locality. Upper beds of the Hudson river group at Wilmington, Illinois, and Iron 

 Ridge, Wisconsin. 



Genus DEKAYELLA, Ulrich. 



Dekayella, ULIUCFI, 1882, Jour. Cin. Soc. Nat. Hist., vol. v, p. 155, and vol. vi, p. 90; 1890, Geol. Surv. 



111., vol. viii, p. 372. 



Zoaria ramose, branches cylindrical or compressed. Zooecia angular or rounded, 

 the shape depending upon the number and disposition of the mesopores. Typically, 

 the mesopores are more or less numerously distributed among the zooocia, and 

 aggregated into irregular clusters. In other cases they may be wanting, except in 

 the clusters, while in some of the earliest forms they are so few as to be practically 

 absent. Acanthopores of two sizes, the large ones, equivalent to those of Dekayia, 

 commence in the axial region, the smaller ones more abundant and developed in 

 the peripheral region only. Diaphragms horizontal, numerous. 



Type : D. obscura Ulrich, Utica horizon of the Cincinnati group. 



This genus includes, so far as known, the earliest types of the family Helerotry- 

 pidai. In the Trenton or more strictly speaking, the Birdseye shales of Minnesota 

 we have, besides species or varieties that are as typical of Dekayella as any occurring 

 in the Cincinnati rocks, two forms that, in having very few mesopores, are more 

 nearly like Dekayia, Edwards and Haime. Tangential sections of the one (Dekayella 

 pnvnuntia var. echinata) very much resemble those of Dekayia aspera Ed. and H., yet 

 when carefully examined, two sets of acanthopores the one large, the other small 

 will be noticed. The abundant tabulation of the tubes is also indicative of Dekayella. 

 The other form (D. prcenuntia var. simplex) is, as the name implies, of a more simple 

 and perhaps the primitive type, with the acanthopores much smaller and scarcely, if 

 at all, separable into two sets. 



The relations existing between Dekayella, Dekayia and Heterotrypa are so intim- 

 ate that I have seriously considered the propriety of throwing them together as one 



