Phylloporlna corticosa.] BRYOZOA. 213 



fronds. In such cases the branches anastomose rather irregularly and are simply 

 convex, not carinate, the median ridge being absent. Fenestrules small, irregular, 

 narrow, often indented by the projecting zocecial apertures. 



Reverse of branches very finely striated, tending, though less strongly than on 

 the obverse face, to form median longitudinal ridges. Fenestrules varying in out- 

 line from elongate-elliptical to subcircular, their width rarely more, usually a little 

 less than that of the branches, their length from one to three times the width ; 

 measuring transversely, six or seven in 5 mm.; longitudinally, the average number 

 in the same space is three. 



Tangential sections, cutting the frond parallel with the plane of its expansion 

 and near the middle of its thickness, show that the branches are generally divided 

 into approximate halves by an obscurely double vertical lamina, thicker than the 

 walls of the zocecial tubes diverging slowly from it toward each side. The tubes 

 have thin walls, are long, and crossed by straight lines representing diaphragms. 

 The number of the latter depends upon age. Where the section divides the tubes 

 just beneath their apertures they are rounded or subangular, with slightly thickened 

 walls, partially separated from each other by solidly filled interspaces or mesopores, 

 that may be considerably smaller or even a little larger than the true zocecia. Here 

 and there, along the middle of the branches, a small acanthopore may be detected. 



Vertical sections show that'the zocecial tubes arise also from a thick, laminated, 

 basal layer, from which they diverge in an upward and outward direction. Their 

 course toward the surface is very gradual in the lower half of the branch, but in the 

 upper half the curve is slightly accelerated so that' their apertures are nearly direct 

 at the surface. Several diaphragms occur in the prostrate or primitive portion of 

 each tube and in young examples (plate V, fig. 10) they may be absent in the more 

 erect superficial portion. With age, however, additional diaphragms, now the 

 diameter of a tube distant from each other, are introduced. Near the surface the 

 tubes separate, leaving obconical interspaces, which are subsequently filled with 

 solid or laminated tissue. 



In transverse sections the branches are subrhomboidal, the lateral diameter 

 being the shortest. The median ridge is shown to be an extension of the double 

 vertical wall already mentioned. Between the two laminae forming this wall, a 

 series of very minute tubuli, similar to those found between the median laminae of 

 many bifoliate Bryozoa, may be observed. On each side of this mesial wall the 

 zocecial tubes are piled over each other, in one or two series, three or four high. 

 These and other characters are well shown in fig. 9 on plate V- 



This is a very remarkable species, and probably the most "comprehensive" 

 type known to me among the Bryozoa. That its place is with Phylloporina will. 



