36 LOWER PENINSULA. 



the stems are usually compressed, elliptical in circumference ; ori- 

 fices very unequal in size. The portrayed specimen is from the Falls 

 of the Ohio, but the same form is also found in the upper limestones 

 of Mackinac Island. Fig. 4 resembles closely form No. 3, and occurs 

 in association with it at the Falls of the Ohio ; its tubes and stems 

 are in all their proportions smaller. On Plate X. casts of this species 

 are represented (Fig. 3) as they occur in the drift. The conical, sub- 

 angular form of the tube channels, the almost total absence of dia- 

 phragms, the dispersed position of the pores, and the mode of 

 gemmation of one tube from the other, are plainly conspicuous in 

 the figures. 



FAVOSITES CLAUSUS, N. Spec. 



Clustered, rapidly branching and anastomosing flexuose stems, 

 varying from one half to one centimeter in thickness. Tubes 

 unequal, the larger ones circular, measuring in different specimens 

 from one half to one and a half millimeter in diameter ; the 

 smaller tubes filling the interstices between the larger ones are 

 subangular. Orifices at the ends of the branches all open ; on the 

 sides of the stems most of them are found closed by opercula. 

 Opercula flat or convex, some of them decorated with twelve 

 marginal carinas radiating toward the centre. Diaphragms partly 

 simple and regular, but largely intermingled with irregular partial 

 septa, formed by the development of lateral squamae analogous to 

 the vertical rows of leaflets in other species of Favosites. Pores 

 numerous. Under this species I comprehend several varieties 

 which closely resemble each other in general structure and mode 

 of growth, but which may possibly be distinct forms. They occur 

 in the Hamilton group and in the corniferous limestone. 



Plate XIV. — Upper left-hand figure represents a silicified speci- 

 men from the Hamilton group of Thunder Bay River, near Broad- 

 well's mills. Similar ramifications arc found in the Hamilton strata 

 of Widder and Arcona, in Canada. The tubes of this form are 

 smaller than in the forms of the Helderbcrg group. The right-hand 

 specimen in the upper row of the plate is from the corniferous 

 limestone found in the drift of Ann Arbor ; its tubes are nearly all 

 of equal size and closed by opercula. 



In the left-hand figure in the lower row, from the Falls of the Ohio, 



