180 PALEONTOLOGY OF NEW YORK. 



This species very nearly resembles some of the forms of Acanthoclema 

 Hamilionmse, but there are fewer ranges of apertures on a branch, the longi- 

 tudinal ridges are stronger, the nodes between the cell apertures are somewhat 

 stronger, and there are no evidences of interapertural pits : from the forms 

 like Acanthoclema scutulalum having straight ridges, it may be distinguished by 

 the stronger ridges, smaller cell apertures and nodes : from Acantholema alter- 

 nalutn, of the Upper Helderberg group, it may be distinguished by its stronger, 

 more prominent, longitudinal ridges, and the less prominent nodes between the 

 cell apertures : from Trematopora (Orthopora) bi-spinulaia by the much stronger 

 and more regular longitudinal ridges. 



Formation and locality. Hamilton group, West Williams, Ontario, Canada. 



Trematopora (Orthopora) tortalinea. 



PLATE L^^, FIG. 9. 



Trematopora tortalhiea, Hai.l. Trans. Albany Institute, vol. x, p. 180. 1881. 

 " " " Report of State Geologist for 1883, p. 10. 1884. 



ZoARiUM ramose, solid, growth usually somewhat sinuous, bifurcations infre- 

 quent; branches frequently diverging at an angle of ninety degrees, diameter 

 from .60 to .75 mm. Cells tubular, septate, arising from the centre of the 

 branch, abruptly curving near the surface, in contact for about two-tliirds 

 of their length. Cell apertures elongate oval, length .20 mm., width usually 

 about one-third the length, but sometimes not more than one-fourth, 

 di.sposed in longitudinal rows, which are sometimes regular and parallel, at 

 other times somewhat irregular ; apertures frequently alternating, forming 

 oblique transverse rows; nine or ten longitudinal rows on a branch ; 

 the surface between them is elevated, forming low, rounded, sinuous or 

 twisted ridges; the longitudinal ridges are marked by small nodes or 

 granules, giving them a serrated appearance. The cell apertures fire indis- 

 tinct and frequently almost entirely obscured by the ridges. When the 

 frond is slightly worn or macerated the longitudinal ridges are indistinct 

 or obsolete, and the obliquely transverse disposition of the cell apertures 

 is the most conspicuous; the frond in this condition presents a very different 

 appearance from that of a well-preserved specimen. 



