CORALS AND BRYOZOA. 245 



Stictopora rectalinea. 



PLATE LXIII, FIG. 23. 



ZoARiDM consisting of a flattened dichotomously branched frond, arising from 

 a spreading base. Branches about 3 mm. in width ; margins parallel, the 

 branches not expanding before bifurcating ; non-celluliferous marginal space 

 very narrow, flat, width about .25 mm. ; transverse section lenticular, 

 abruptly narrowing near the margins, the remaining portion regularly con- 

 vex, greatest thickness .75 mm. ; bifurcations comparatively distant, branches 

 diverging at an angle of about forty-five degrees. Cells tubular, cylindrical, 

 for about one-half their length parallel with the axis, then abruptly turning 

 and opening almost directly outward ; the marginal cells are a little oblique 

 to the axis of the branch, the others are parallel. Intercellular tissue vesicu- 

 lose ; vesicles irregularly disposed, more compactly arranged near the surface 

 than below. Cell apertures oval, length about .20 mm., width a little more than 

 one-half the lengtii, sometimes two-thirds, disposed in parallel longitudinal 

 rows, eleven or twelve rows on each face of the branch ; marginal apertures 

 larger and more nearly circular than the others ; apertures separated longi- 

 tudinally by a space about equal to their diameter ; in the central rows 

 there are fourteen in the space of 5 mm., in the marginal rows there are 

 eight or more in the same space. Peristomes thin, in the central rows, scarcely 

 elevated, with evidences of two slight denticulations within the outer margin. 

 The apertures frequently appearing immersed ; approaching the margin the 

 peristomes become more distinct, the outer portion being the most strongly 

 elevated and denticulated. The space between the rows of apertures is a 

 little more than twice the width of an aperture, convex or sub-angular and 

 striated : the striae are very fine, minutely granulose, three or four between 



adjacent rows. 



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



