136 LOWER PENINSULA. 



having the form of low crests in the inner circumference of the pits, 

 but of rounded rugose form in their extension across the interstices, 

 and on the sloping sides of the monticules. The surface of the 

 polyparia is generally raised into irregular large blisters, which 

 impair the distinctness and continuity of the radial plications. In 

 vertical sections layers of interlaced coarse vesicles are found to 

 constitute the whole polyparium. 



Occurs in the Niagara group of Point Detour, and also in Iowa 

 localities. This form is easily mistaken for Strombodes mamillatus, 

 Owen, which occurs in its association. The well-developed flat 

 diaphragms and entirely vesiculosa structure distinguish it, how- 

 ever, from the latter. 



Plate XLIX. — P'ig. 4 represents a surface view of a silicified spec- 

 imen from Point Detour. 



CYSTIPHYLLUM, Milne-Edwards. 



Simple or loosely aggregated polyp cells, of conical or cylindrical 

 form, enveloped by an epithecal wall, composed of an invaginated 

 series of cell cups of compound vesiculose structure, and radi- 

 ated by plications. The plications are either crest-like within the 

 ascending part of the calyces, and dilating into flattened broader 

 rugae toward the peripheral margins, or are represented merely by 

 superficial linear striae or rows of spinules ; they often become totally 

 obsolete, and the surface of the calyces appears simply blistered, 

 without any visible radiation ; in no case do the plications com- 

 bine into vertical laminae pervading the whole length of the coral- 

 lum. The arrangement of the plications into four principal fas- 

 cicles is in some of the specimens very distinct. The inner area 

 of the polyp cells is rarely intersected by transverse diaphragms ; 

 generally the central vesicles are somewhat coarser than the 

 peripheral ones, but without demarkation between the bottom part 

 of the calyces and the sides as in Cyathophyllum. The exterior 

 epithecal wall is in many specimens longitudinally ribbed by well- 

 pronounced septal striae, while the vesiculose internal surface of 

 the calyces may exhibit but very indistinct radial plications. 



