58 LOWER PENINSULA. 



cling orificial pits, but the body portion of the orificial walls spreads 

 into a common interstitial surface, and the front walls project as 

 sharp semicircular lips. Transitions from one of the surface characters 

 described into the other can be followed out in nearly every larger 

 specimen. The end branches generally differ somewhat from the 

 older stems, and the orifices of the upper surface of the prostrate 

 expansions are not quite alike to those of the under side. The di- 

 lated orificial pits are nearly always wider in the transverse direc- 

 tion of the stems than in the vertical ; their diameter is about one 

 and a half millimeter ; that of the inner tube channels about one 

 third to one half millimeter. Pores distant. Diaphragms sparingly 

 developed. From the former species, this one differs in having 

 smaller tubes, and less compressed, nearly circular orificial open- 

 ings ; but great similarity exists between them, and by reason of 

 the great variability in the surface structure of both, it is sometimes 

 hard to tell to which class certain specimens belong. 



Plate XXII., Lower tier. — The three left-hand figures are silici- 

 fied fragments from the Falls of the Ohio, representing a few of the 

 modifications in which the species occurs. 



STRIATOPORA, Hall. 



Ramose stems, composed of thick-walled conical tubes, opening 

 on the surface with oblique dilated orifices, in all particulars cor- 

 responding with the structure of Cladopora, from which they mainly 

 differ by a cycle of longitudinal furrows radiating across the ex- 

 panded tube margins, a difference which, as previously remarked, is 

 not at all peculiar to Striatopora, but belongs to the essential family 

 characters of all Favositoids, and happens to be more obviously 

 developed in the forms called Striatopora than in the next related 

 Cladopora. In addition to the longitudinal furrows, the inter- 

 mediate band-like spaces also sometimes bear rows of spinules ; 

 and as another peculiarity in Striatopora, the abundant develop- 

 ment of, lateral pores may be mentioned. 



STRIATOPORA HURONENSIS, N. Sp. 



A single fragment of a stem eight millimeters in diameter is the 

 only specimen I have seen ; but as being one of the first representa- 



