142 LOWER PENINSULA. 



noticeable, and sometimes also the lateral septal gaps are well 

 marked. In vertical sections the centre of the polyparia is found 

 to be intersected by well-developed transverse diaphragms ; the 

 vertical crests intersecting them divide the interstices between 

 them into irregular cell spaces. The apices of the polyparia are 

 pointed, and rarely exhibit a small scar of attachment. Sometimes 

 twin cells are found, but this is abnormal. 



Plate LI., Upper row. — The largest specimen is from the Hudson 

 River group of Drummond's Island ; the other six smaller speci- 

 mens were found at Richmond, Indiana, and at Madison. The 

 right-hand calyces have broad convex cup bottoms with irregularly 

 entangled lamellae ; the two upper figures to the left of the larger 

 have a well-developed septal fovea, and a narrow, styliform, central 

 protuberance. The lower left-hand specimen is a twin-cell. 



STREPTELASMA PATULA, N. Sp. 



POLYDILASMA, Hall. 



Short conical polyparia, about two centimeters wide at the ex- 

 panded calyx margins, by a length of only one or one and a half 

 centimeter. Calyx variable in depth in accordance with the more 

 elongate or shortened external form of the polyp cells, surrounded 

 by from twenty-five to thirty stout lamellar crests, with as many 

 smaller intermediate ones, confined only to the marginal portions 

 of the calyces. The sides of the lamellae are transversely striate, 

 and their edges crenulated. By the convergence of the lamellae 

 in the centre, a narrow columellar axis of spongiose structure is 

 formed, which on one side is deeply exsinuated by a septal fovea ; 

 in very young specimens this axis is a horseshoe-formed erect leaf, 

 against the circumference of which the converging lamella; abut ; 

 the centre of the horseshoe sinus is occupied by a strong lamella. 



Found in the Niagara group of Drummond's Island and Point 

 Detour; also in the Niagara limestones of Iowa, at Masonvillc. 



Plate XXXIX. — Fig. i represents a number of silicificd speci- 

 mens found at Drummond's Island. 



