122 LOWER PENINSULA. 



area is occupied by a flat diaphragm free of crests. I was at first 

 inclined to consider the latter form "as a separate species, but I 

 found later that these differences constitute only individual vari- 

 ations of the same form. 



Found in the Niagara group of Point Detour, Scul Choix, on 

 Lake Michigan, and in the drift boulders of the Lower Peninsula. 



Plate XLV. —Fig. 3 is a specimen with plainly developed trans- 

 verse diaphragms ; in Fig. 4 the lamellae extend to the centre, 

 and the diaphragms are obscure. Both specimens are found in the 

 drift of Ann Arbor. 



DIPHYPHYLLUM SIMCOENSE, Billings. 

 Synon., Eridophyllum Simcoense, Billings. 



DIPHYPHYLLUM STRAMINEUM, Billings. 



Colonies of cylindrical, subparallel, straight or flexuose stems, 

 closely aggregated or more distant from each other, varying in 

 different specimens in diameter from three to six millimeters. 

 Surface longitudinally ribbed and annulated by wrinkles of growth. 

 The stems laterally connect by slender transverse processes, similar 

 to the transverse tubules of Syringopora— not, however, making 

 communication between the visceral cavities, as in those, but 

 merely fastening externally to the walls for mutual support, ac- 

 cording to the necessity ; in some places these are numerous 

 and crowded, in others considerably distant. Calyces deep, with 

 erect sides and slightly dilating margins, surrounded by about 

 forty crenulated lamellae of equal size near the margins, but alter- 

 nately longer and shorter in the bottom part of the calyces. In 

 some specimens these are almost totally restricted to a narrow 

 marginal cycle, and the centre is occupied by flat, broad dia- 

 phragms with depressed circumference ; in other specimens the 

 larger lamellre extend nearly or completely to the centre, and in- 

 tersect the diaphragms as continuous vertical leaves. The same 

 specimens often exhibit tubes with both variations of structure, 

 plainly demonstrating how little importance can be placed in some 

 cases on the degree in development and extension of the vertical 



