Monotrypa (? Chaetetes) cumulata.] 



In the absence of any knowledge of the interior the generic position of the 

 species is necessarily a little doubtful. In a general way, M. nodosa resembles 

 Leptrotypa filiosa d'Orb. sp., of a lower horizon in the Hudson river rocks, very closely, 

 and the principal difference that can now be pointed out is in the size of the zooecia, 

 that species having eleven or twelve apertures where the present form has nine or 

 ten. But Atactoporella ortoni Nich. sp., to which Whitfield referred the Wisconsin 

 specimens, is a delicate parasitic form totally distinct. 



Formation and locaUty.— Common In the upper beds of the Hudson river group at Iron Ridge and 

 Delafleld, Wisconsin, and Savannah, Illinois. 



Mus, Beg. No. 7574. 



MONOTEYPA ( ? Ch^TETES) CUMULATA, W. SJB. 

 PLATE XXVII, FIGS. 26 and 27. 



Zoarium forming small subglobular or irregular masses, generally consisting 

 distinctly of irregularly superposed layers ; average &,izes between 15 and 20 mm. in 

 diameter, anything under or over those extremes being rare ; no monticules. 

 Zooecial walls thin ; apertures polygonal, of unequal sizes, sometimes forming at 

 long but irregular intervals large clusters in which they are conspicuously larger 

 than elsewhere ; in most cases however the apertures are subequal, with an average 

 of six and one-half or seven in 3 mm. Mesopores and acanthopOres wanting. 



Internal characters: In vertical sections the tubes diverge rapidly and rather 

 irregularly, and their walls present an obscure longitudinal lineation. Diaphragms 

 occur at intervals varying from one to four times their diameter, but their position 

 in neighboring tubes corresponds approximately. In transverse sections the prin- 

 cipal interest attaches to the structure of the walls. In most sections the wall 

 is comparatively thick and seems to be composed of minute columns which, being 

 cut transversely, appear as alternately dark and lighter parts. In this respect the 

 structure of the walls is essentially the same as in true Chcetetes, and I would un- 

 hesitatingly have placed the species into that genus had I been able to satisfy 

 myself that the phenomena observed were not the result of secondary causes. 

 Namely, in some sections the appearance is very different, the wall itself being more 

 sharply defined and thinner than usual (especially where the tubes are filled with 

 matrix instead of calcite) and without the alternating light and dark spots. But 

 where the tubes are filled with calcite the latter for some distance inward from the 

 wall is of a darker color than at the center, and exhibits, strange to say, a spotting 

 not unlike that pertaining to the wall itself in other sections. 



