146 LOWER PENINSULA. 



ZAPHRENTIS UMBONATA, N. Sp. 



Conical, horn-shaped polyparia resembling Zaphr. Stockesii, at- 

 taining in some larger specimens a calyx diameter of eight centi- 

 meters by twice that in length ; the usual size of the specimens 

 found is smaller. Calyces spacious, with erect acute margins and 

 a broad bottom, which is reversed into a large, laterally compressed, 

 prominent cone. The circumference of the larger calyces is sur- 

 rounded by about eighty large lamellae, with as many intermediate 

 smaller ones ; the larger ones unite on the central cone, ascending 

 its sides directly or with a spiral twist. A large septal fovea is 

 developed in the median line of the larger curved side. In vertical 

 sections the invaginated, reversed, conical cell bottoms are observed 

 to have grown together with their apices and to form a cellulose, 

 ■ pseudo-columella. Found associated with Zaphr. Stockesii in the 

 Niagara group of Point Detour and Drummond's Island. Casts 

 of a similar species are common in the Niagara limestones of 

 Milwaukee. At Louisville, also, this coral occurs. 



Plate LI., Lower tier. — The upper figure in the centre is one of 

 the smaller-sized specimens found on Drummond's Island ; another 

 small specimen is represented in the lower right-hand corner of the 

 plate. The central cone is in some specimens much more prom- 

 inent than in those given here. In the lower row of the same 

 plate the first outer specimen on the left-hand side and the third 

 one represent other calyces of a Zaphrentis, conformable in some 

 respects with the heretofore described associated forms, but differ- 

 ing in the shape of the cell bottom, which in one is formed by a 

 large rounded protuberance, exsinuated on one side by a septal 

 fovea, while in the other, evidently only an individual modification 

 ■of the former, it is a horseshoe-formed elevated ring with a deeply 

 (depressed, smooth, central excavation. This form seems to con- 

 stitute a different species from the others, but I leave the question 

 open for further decision. 



ZAPHRENTIS GIGANTEA, Lesueur. 



Conico-cylindrical, horn-shaped polyparia, attaining in some speci- 

 mens a size of two and a half feet in length, by a diameter of three 



