Il8 LOWER PENINSULA. 



the lamellae may extend over it as carinations, becoming twisted in 

 the centre. On the ascending sides of the calyx the lamellae have 

 the form of acute linear laminae alternating in size, a smaller and a 

 larger one near the bottom of the calyx always vmited into pairs. 

 In the marginal portions of the calyces, the two plates forming the 

 linear crests diverge at the base, and open into a tent-shape. The 

 four septal foveaeare scarcely ever distinct — two of them, or it may 

 be only one, being plainly developed. 



The centre of the polyparia is, in vertical sections, seen regularly 

 intersected by large transverse plates, and the continuity of the 

 vertical crests is interrupted. Number of lamellae in calyces of six 

 or seven centimeters diameter from one hundred to one hundred 

 and ten. Associated with the elongated type form already de- 

 scribed, which is represented on Plate XLIV., lower row, right- and 

 left-hand specimens, are shorter conical specimens, w^ith broad, ex- 

 panded calyx margins, and generally with a very prominent bot- 

 tom, covered by twisted radial crests, seeming to be a mere variety 

 of the former kind. The central figure between the two repre- 

 sents one of them. Occurs in the Niagara group of Drummond's 

 Island, etc. 



OMPHYMA STOCKESII. 



Synon., Ptychophyllum Stockesii, Milne-Edwards. 



Conical polyp cells very similar to the former species, in structure 

 and mode of growth. Calyces spacious, rather shallow, with ex- 

 panded margins ; bottom of cells always raised into a monticule, 

 on vv'hich the lamellae unite in twisted manner. Two of the septal 

 foveae distinct, the other two obscure. Lamellae united into pairs 

 of a larger and a smaller one ; of more delicate structure than in 

 the former kind, and with narrower interstices. Their vertical con- 

 tinuity is complete in an inner intermediate cycle ; interrupted in 

 the central part, occupied by transverse diaphragms, and in the 

 marginal parts, in which the horizontally expanded cup membranes 

 are bent into zigzag lines, and superimposed in layers. Number of 

 lamelljE somewhat larger than in the former species in specimens 

 of the same size. External surface covered with root-like ex- 

 crescences as in the other. The description given by Edwards of 



