152 LOWER PENINSULA. 



by a length of one decimeter. Calyces of that size are surrounded 

 by 170 or 180 alternately small and large lamellse, which are, within 

 the cups, sharp linear crests, but become lower rounded rugae on 

 the margins of the cup walls. End cups deep, with erect, acute 

 margins, of the shape of elongated troughs, gradually diminishing 

 into a narrow bottom, one side of which is deeply depressed by a 

 septal fovea situated on the median line of the longer diameter of 

 the compressed calyces. The degree of compression is not in all 

 specimens equally strong ; some are very nearly flattened on the 

 compressed sides, while others have a convex oval circumference. 

 The surface of the polyparia is annulated by irregular rounded rugae. 



Found in the upper Helderberg limestones of the Falls of the 

 Ohio. It resembles the former species, but is much larger, and is 

 easily distinguished by the position of its septal fovea, which is on 

 the narrow side, while that of the previous form is in the centre of 

 the broader side. 



Plate LIII., Lower tier. — The upper second figure from the 

 right-hand side. I consider it desirable to give a figure and descrip- 

 tion of this form, not found in Michigan up to the present date, 

 but in all probability to be discovered some day by industrious 

 collectors. 



Various other species of Zaphrentis, partly already known and 

 described (Zaphrentis Rafinesqui, Milne-Edwards), partly new 

 forms, are omitted from this report, as not found within the bound- 

 aries of the State of Michigan. 



ZAPHRENTIS SPINULOSA (?) Milne-Edwards. 



Symmetrically curved, conical polyp cells, attaining a length of six 

 centimeters by a calyx diameter of three centimeters. Calyces 

 deep, with erect margins, surrounded by about forty-five stout 

 lamellae, and as many rudimentary intermediate folds near the 

 margins of the calyces. A large septal fovea is developed on the 

 concave side of the horn-shaped cells, and besides the two lateral sep- 

 tal gaps, are generally well marked in the specimens. The surface 

 of the polyp cells is annulated by rings of growth, and the basal 

 portion is decorated by stout spinules similar to those of Zaphr. 

 spinulosa, Milne-Edwards. I have not seen any of the Western 

 specimens with suf^ciently well-preserved open calyces to enable 



