190 PALEONTOLOGY OF NEW YORK. 



ACANTHOCLEMA, Hall. 1886. 



(See page 72.) 



ACANTHOCLEMA SCUTULATUM. 



PLATE LV, KIGS. lS-17 ; AND PLATE LVI, PJ(iS. 19, 20. 



Tremalapora acniiilata, Mku.. Trans. Albany Institute, vol. x, p. 180. 1881. 

 " Report of State Geologist for 1883, p. 7. 1884. 



ZoARiUM ramose, bifurcations infrequent ; branches diverging at an angle of 

 from sixty to ninety degrees, diameter about .70 mm. Cells tubular, 

 arising from a filiform axis at the center of the branch, in contact for the 

 greater portion of their length, oblique to the surface and very slightly 

 curved. Cell apertures oval, length on different fronds from .18 to .25 mm., 

 width about .10 mm., disposed in longitudinal, parallel rows, those of adja- 

 cent rows alternating and forming oblique transverse rows, the latter 

 arrangement being usually the most conspicuous. Peristomes very thin, 

 slightly elevated, or entirely obsolete. The longitudinal ranges are sepa- 

 rated by ridges, which generally unite between the cell apertures, enclosing 

 them in a rhomboidal, vestibular area, and having at their junction a prom- 

 inent, conical, hollow node. When the frond is well preserved the surface 

 between the cell apertures is apparently solid ; when slightly worn or 

 macerated there is a crescentiform opening at the base of each aperture. 

 There is a short tubule longitudinally between adjacent cells. 



This species very closely resembles A. allernatum, of the Upper Helderberg 

 group, but it is usually a little larger, the longitudinal ridges and nodes are 

 more prominent, the ridges are nearly always sinuous and unite between 

 the cell apertures, while in that species they are generally straight. From 

 Trimatopora (Orthopora) reticulata it may be distinguished by its more elongate 

 cell apertures, the less angular and smooth longitudinal ridges ; internally tlie 

 structure is very different : from T. (0.) subquadrata it is distinguished by its 

 much more slender branches, its more elongate-oval cell apertures and by the 

 rhomboidal, vestibular areas From T. (O.) rhombtfera, of the Lower and Upper 

 Helderberg groups, it is distinguished by its more elongate-oval cell apertures 



