SCRUPARIA. 23 



have laid down for the definition of genera in this family be 

 correct, we can hardly hesitate to place the species under 

 consideration in different groups. 



The plan of the ramification in S. clavata, involving, 

 as it does, the frequent occurrence of a biserial arrange- 

 ment of the zooecia as in Gemellaria, and involving also 

 the remarkable position of the ovicelligerous cell, is, 

 in my judgment, a generic character. The difference 

 in the structure of the aperture is also important. 

 Scruparia is, I believe, as distinctive a form in its way 

 as Gemellaria. 



It may be regarded as intermediate in some respects be- 

 tween the last-named and Eucratea. In different states it 

 presents the arrangement of the cells which is characteris- 

 tic of each of these genera : in some cases they are simply 

 uniserial ; in others two lines of cells are united back to 

 back, and we have the general form of zoarium which be- 

 longs to Gemellaria. Perhaps the uniserial is the more 

 common condition; but intermingled with tall and well de- 

 veloped shoots of this class there are generally others which 

 have assumed either wholly or in part the biserial character. . 

 Frequently a shoot occurs in which a few of the cells have 

 others placed back to back with them, while the rest form 

 a single series. A remarkable change also takes place in 

 the cells which are united in pairs : they lose the elongated 

 form which belongs to the uniserial class, and become 

 shorter and less slender in habit, so that the biserial shoots 

 present a very striking contrast in appearance to the uni- 

 serial. The cells which carry the ovicells are, as in the 

 genus Eucratea, partially developed ; they are very short 

 (about half the size of the ordinary cells) , and have lost al- 

 together the characteristic form of the species. They are 

 always placed back to back with another cell, except in the 

 case of biserial shoots, on which they are often, though 



