BRYOZOA. 127 



Bnmidlotya.l 



primitive portion of the zooecia as sharply defined, thin-walled, oblong-quadrate 

 spaces, the end walls of which, while approximately at right angles with the long- 

 itudinal lines at the center of the zoarium, gradually assume an oblique upward direc- 

 tion toward the sides. (Uompare plate VI, fig. 1 3.) The next condition is when the 

 anterior wall or side of the zooecium becomes convex, while the posterior side begins 

 to extend over the cell till at last the oval aperture is formed. Now the anterior 

 and posterior walls are no longer recognizable in the section, but the division between 

 the longitudinal walls is clearly marked by a dark line, that, when the preservation 

 of the specinien is sufficiently favorable, will be noticed to consist of a connected 

 series of minute tubuli. Besides these, an occasional dark spot or tubulum may be 

 noticed in the end spaces. Most of the stages so far described are shown in fig. 13, 

 on plate VI, and all further phases are to be classed as old conditions. They consist 

 principally of an increase in the number of minute interstitial tubuli. (See plate 

 VI, figs. 1 and 4.) 



The above description does not include two forms that deserve recognition as 

 varieties. Their peculiarities are not sufficiently constant to entitle them to the 

 rank of species. In my preliminary report on the Minnesota Bryozoa Hoc. cit.) 

 another form of the species was separated as var. minor. The better and much 

 more complete material since studied proves, however, that the specimens so desig- 

 nated are merely young examples and therefore not deserving of a distinct name. 



Var. Major Ulrich. 



The zoarium in this variety is more robust, the branches being wider, in some 

 cases attaining a width of over 8 mm.; usually the thickness is also greater, but thin 

 examples are not uncommon. Perhaps the chief peculiarity of the variety is found 

 in certain grano-striate or smooth spots', which occur at rather irregular intervals 

 along the center of the branches. The internal structure agrees in all essential 

 respects with that of the typical form of the species, the only feature not seen in the 

 latter being the solid maculae. 



Mus. Reg. No. 5940. 



Var. Senilis, n. var. 



PLATE VI, FIGS. 2 and 3; PLATK VII, FIGS. 16 and 17. 



In this rather rare form the general appearance of the zoarium is like that of 

 well developed examples of the typical variety. On comparison, however, it is found 

 that the non-celluliferous margin is unusually wide and sharply defined. Connected 

 with this are certain narrow, irregular or subelliptical, depressed spaces just within 

 the axes of bifurcation. A more important peculiarity is presented by the zooecial 

 apertures. These, generally, instead of being placed in longitudinal furrows[](as 



