CORALS AND BRYOZOA. 263 



regularly disposed in parallel longitudinal rows, eight rows on each face of 

 the branch ; the apertures of the marginal rows are larger than the others, 

 having a length of .30 mm., and are oblique to the axis of the branch. 

 Peristomes thin, slightly and equally elevated, not denticulated, and when 

 well preserved granulose. Between adjacent cell apertures, in a longitudinal 

 direction, are two minute pits, arranged laterally, partitions very slightly 

 elevated ; in the course of growth these pits form minute tubuli between 

 the cell tubes. The peristomes are laterally wholly or partially in contact, 

 according as the apertures are opposite or alternate, and coalesce, giving to 

 the ranges of apertures the appearance of being separated by comparatively 

 prominent granulose ridges. 



********* 



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



T^NIOPORA, Nicholson. 1874. 



TiENIOPORA EXIGUA. 



PLATE LXn, FIGS. 15-26. 



TcBtMtpora exifftM, Niciiolsox. Pateontology of Ontario, p. 108. 1874. 

 " " Hall. Trans. Albany Institute, vol. x, p. 192. 1881. 



Ptempora duogerierLt, Hall. Trans. Albany Institute, vol. x, p. 192. 1881. 

 Twniopora exiffita. Hall. Report of State Geologist for 1883, p. 49. 1884. 



ZoARiUM ramose, flattened, proceeding from a spreading base, or from rootlets 

 attached to foreign bodies ; branches triangular or flattened. The branches 

 of the lower portion of the frond are usually triangular, although this condi- 

 tion may occur on all portions of the frond, sides concave, equal or nearly so, 

 width 3 mm. or a little more ; from each angle proceed depressed quadran- 

 gular branches, which both bifurcate and ramify laterally, continuing growth 

 in the same manner as the parent branches; the flattened branches are 

 from a little less than 3 mm. to 4 mm. wide, with parallel margins, not 

 expanding before bifurcation ; non-celluliferous marginal space flat, smooth, 

 width from .33 to .50 mm. ; transverse section rhomboidal, sometimes 

 abruptly contracted near the margin, angular at the middle, with a prominent 



