DESCRIPTION OF THE GENERA AND SPECIES, &c. 
In the foUoAvhng specific descriptions I have followed the same system as that which 
was adopted in the case of the Simple Ascidians described in Part I. of this Eeport. 
The only point which requires special explanation is the method of measurement which I 
have employed, and which is shown in the accompanying diagrams. 
In the case of a sessile massive colony, such as the one in fig. 5, the “length,” 
AB, is the distance from the point of attachment, B, to the highest point on the top of 
Fig. 5. — Diagram of a sessile massive colony to show the length (AB), the breadth (CD), and the thickness (EF). 
Fig. 6. — Diagram of a stalked colony to show the “ head,” the “ peduncle,” and the various measurements. 
the colony, A ; the “ breadth,” CD, is the greatest horizontal diameter, and the thickness, 
EF, is the greatest (or the average) diameter at right angles to CD, not necessarily in 
the same plane. In the case of a pedunculated colony (see fig. 6) the dimensions of 
the “head” and of the “peduncle” are given separately. AB is the length, CD the 
breadth, and EF the thickness of the head ; while GH is the length and KL the 
thickness of the peduncle. The length and the breadth are, except when the contrary is 
stated, the extreme length and breadth, but the thickness is usually the average or most 
