15: 



LOWER PENINSULA. 



me to establish their exact identification with the Michigan speci- 

 mens. 



Occurs in the carboniferous limestones of Saginaw Bay, on Point 

 aux Grees, and on Charity Islands ; likewise in the limestones of 

 Bellevue, Eaton Co. 



Plate LV., Lower row. — The upper four central figures and the 

 larger calyx to the left of them represent specimens found at 

 Bellevue, Michigan. 



AMPLEXUS, SowERBY. 



I can not find an appreciable difference between the genera 

 Amplexus and Zaphrentis ; both have the same general structure. 

 The radial plications in Amplexus are said to be confined to the 

 marginal parts of the polyp stems, and not to extend far across the 

 central area, principally built up of transverse diaphragms. But it is 

 not uncommon to see, in so-called specimens of Amplexus, the 

 radial crests extending to the centre of the diaphragms, under the 

 form of low superficial carina. On the other hand, it is equally 

 common to notice genuine Zaphrentis forms in which the radial 

 crests are confined to a peripheral c>'cle, and do not reach to the 

 centre. 



Amplexus generally grows in elongate cylindrical stems, while 

 Zaphrentis has more of a conical mode of growth, but this is also 

 a very vague difference ; Zaphrentis frequently grows likewise in 

 cylindrical stems, and among the associated forms of Zaphrentis 

 gigantea, Zaphr. Rafinesque, and Amplexus Yandelli, such a simi- 

 larity in stj^ucture exists that fragments of stems of the three species 

 are never distinguishable from each other with perfect security 

 from mistakes. In some forms of Amplexus the septal fovea 

 becomes obsolete, and in polyp stems where a septal fovea exists 

 it is not as well marked in one part as in another. The genus 

 Calophyllum, Dana, has been created to include these forms de- 

 prived of a septal fov^ea, but I consider such distinction superfluous. 



AMPLEXUS SHUMARDI. 

 Synon., CvATHOi'ii, Siiumardi, Milne-Edwards. 

 Articulated cylindrical pol)'p stems, composed of a succession of 



