BRYOZOA. 143 



Phyllodlctya.] 



drawn out anteriorly, with the posterior edge abrupt and slightly elevated, arranged 

 in straight or curved, diagonally intersecting lines, and, less obviously, in longitudinal 

 series, with about seventeen in the former and twelve in the latter in 5 mm. Inter- 

 spaces separating the apertures in the diagonal rpws narrower than the apertures, 

 while those between their ends may be wider and concave instead of rounded, with 

 the posterior rim extending up along their sides. When in a good state of preserva- 

 tion a row of minute papillae crowns this rim, and thus extends around the posterior 

 margin of the zocecial apertures and up their sides to the row belonging to the suc- 

 ceeding aperture. There are therefore two rows of these papillae between neighbor- 

 ing apertures, but it is not uncommon to find the spaces between the apertures in 

 the diagonal rows too narrow for their full development, and then they are crowded 

 into an irregular single row. 



In vertical sections the zocecial tubes begin with a rather long prostrate cell 

 from which they proceed to the surface by a gentle outward curve ; the continuance 

 of this curve causes the apertural portion of the tube in old examples to be much 

 more nearly direct to the surface than in their younger stages. In an average 

 example a line drawn from the aperture to the proximal extremity of a tube forms 

 an angle of about 35 degrees with the central laminae. Complete diaphragms to the 

 number of five have been observed to cross each tube. Near the central axis the 

 walls are thin, but soon they begin to spread, admitting of the intercalation of from 

 three to five successive vesicles. Above these the interspaces are filled with solid 

 matter, seemingly structureless except for the minute dark tubuli traversing them 

 in a direction at right angles to the plane of the zoarium. These tubuli arise in a 

 dark line running along the posterior side of the tube. 



Tangential sections show a considerable deposit of solid material on the inner 

 side of the tubes. This is scarcely to be described as ring-like, since it is not sharply 

 defined nor of equal thickness all around, being widest and rather indistinct anteri- 

 orly, and but illy distinguished at any point from the interspaces. The latter are 

 occupied by minute dark spots (median tubuli) in single or double rows, representing 

 and corresponding with the arrangement of the minute superficial papillae described. 



The above description is based almost entirely upon the specimen mentioned as 

 having been received from Prof. C. W. Hall. Its characters, as has been stated, agree 

 very closely with one type of P.frondosa, but not nearly as well with the other, pos- 

 sibly distinct form, originally united with it. Compared with P. varia, to which I 

 shall provisionally refer nearly all of the Minnesota specimens of Phyllodidya so far 

 seen it will be found to differ in having thinner interspaces, and larger apertures, 

 with the diagonal instead of the longitudinal arrangement predominating. Further 



