ZooL.— Vol. III.] ROBERTSON— ASCORHIZA OCCIDENTALIS. I05 



simple Ascidians, and were probably collected for such. 

 Two regions are well defined — an upper, expanded portion 

 containing actively functioning polypides, and a lower, stem- 

 like portion, whose function is mainly supporting. One of 

 these colonies is represented in fig. 8. It rests on a small 

 disk ((^.) from which there grows a solid stalk-like portion 

 {j)ed.), in this instance occupying about a third of the 

 whole height of the colony. The remaining two-thirds 

 consist of the nutritive and reproductive animals whose 

 zooecia form a single-layered, gelatinous, bag-like structure. 

 In other specimens the stalk is shorter and more distinctly 

 differentiated. Fig. 9 represents such a form. 



In cross-section the stalk is circular, and consists of a 

 solid mass of zooecia radially arranged, many of which con- 

 tain functioning polypides. The cuticle is brown and some- 

 what thickened, and acquires a few wrinkles. No structures 

 corresponding to the myoecia of Ascorhiza occur, the 

 zooecia of the stalk never losing their primitive character. 

 The expanded upper portion varies in height from one to 

 two inches. The surface is smooth, the zooecia are im- 

 mersed, forming usually a single-layered bag, the interior 

 of which is filled with a loose tissue. 



The form and arrangement of the zooecia connects this 

 species with Alcyonidium, while the possession of a stalk 

 relates it to Ascorhiza. It lacks, however, an important 

 character of the Ascorhizan stalk. There are not only no 

 muscular elements in the stalk, but in the head there is no 

 region where the distinctively peduncular elements are pro- 

 duced, such as Ascorhiza possesses. 



The possession of a peduncle distinguishes this species 

 from other known Alcyonidia, and seems to be a constant 

 character. It will serve, therefore, as the basis for a new 

 species, Alcyonidium -pediinculatiini, which will occupy a 

 position intermediate between other erect Alcyonidia and 

 Ascorhiza. In order to receive these two new members, 

 viz., Ascorhiza occidentalis and Alcyonidium ■pedwnculatutn , 

 the definition both of the family Alcyonidiidas, and of the 

 genus Alcyonidium will have to be broadened somewhat. 

 Accepting the definition of the family given by Hincks in 



