292 MYRIOZOID^. 



of the last-named) and much stouter habit, by the very- 

 regular transverse ribbing of the zocecia, and by the 

 calcareous expansion which in greater or less degree 

 borders the latter and the connecting tubular stem. 



I have met with H. expansa in two very different con- 

 ditions. In one the zooecia are massed together, and the 

 lateral expansion is much developed, and forms a connect- 

 ing crust, which fills up the spaces between the cells and 

 unites them together. In this form the branches origi- 

 nate, as IVIr. Norman has remarked, from the side of a 

 cell at a very slight angle. From the masses thus pro- 

 duced linear series of cells are given off, which sometimes 

 anastomose and form an irregular wide-meshed network. 



In the other condition H. expansa exhibits a very 

 regular growth, having much the same habit as Aledo 

 granulata. The zooecia range in single lines and bifurcate 

 frequently, two cells in each case arising from the top of 

 the terminal cell of the series. In this form the calca- 

 reous edging is almost if not entirely wanting ; there 

 seems to be great variability in this character. When 

 fresh the cells are beautifully hyaline and glossy, and 

 very finely lineated longitudinally. The ovicelligerous 

 cells, which are exceedingly small, are generally attached 

 by a short stem to the side of another cell, as is usual in 

 this genus. In all cases the tubular prolongation of the 

 zooecium seems to be of very moderate length in this 

 species ; and very commonly it is quite rudimentary. 



Dr. Dawson was the first to notice and describe this 

 form; but the list of Polyzoa in which he published it, 

 included under a more general title and imbedded in a 

 volume of the Canadian Survey Reports, escaped obser- 

 vation, and it was subsequently redescribed by Norman, 

 who gave it the same name as its original discoverer. It 

 is much more characteristically American than British, 



