36 
THE VOYAGE OF H.M.S. CHALLENGEE. 
means generally accepted, was really worthy of being regarded as a distinct genus. Della 
Valle consequently divided the family into three genera;^ — Botryllus, Polycyclus, and 
Botrylloides. In his elaborate work on the Compound Ascidians of the Gulf of Eovigno, 
published in 1883, von Drasche adds a fourth group, Sarcobotrylloides, for forms which 
bear the same relation to Botrylloides that Polycyclus does to Botryllus. His classifica- 
tion of the Botryllidse is as follows : — 
Family. 
Botryllid^, 
Genus. 
I Botryllus, 
( Botrylloides, 
Subgenus. 
Polycyclus. 
Botryllus. 
Sarcobotrylloides. 
Botrylloides. 
This arrangement seems to agree fairly well with the present knowledge of the group, 
and as the specimens in the Challenger collection can all be referred to one or other of 
these groups, the only modification which I suggest is that the four subgenera should be 
regarded as distinct genera. They seem to me to be nearly equidistant from one another, 
and I think it would be quite as natural to unite Polycyclus and Sarcobotrylloides, the 
two massive groups, and distinguish them from Botryllus and Botrylloides, the two 
incrusting groups, as to adopt von Drasche’s arrangement. Consequently it seems better 
to avoid the unnecessary complication of recognising groups of two ranks between the 
species and the family, and simply to consider the Botryllidse as including four genera : — 
Botryllus, Gaertner and Pallas. 
Polycyclus, Lamarck. 
Botrylloides, Milne-Edwards. 
Sarcobotrylloides, von Drasche. 
It is a remarkable fact that the common genus Botryllus is not represented by any 
specimens in the Challenger, “ Porcupine,” or “ Lightning ” collections. This is partially 
explained by Botryllus, in the restricted sense, being almost entirely a shallow water 
genus, most of the known species being found at or about low water mark on coasts, 
while the dredging operations of these expeditions were mainly carried on in deep water. 
Still a good deal of shallow water investigation was done by the Challenger at some 
localities, such as Port Jackson, Kerguelen Land, the Philippine Islands, and Japan, and the 
total absence of species of Botryllus from the collections seems to indicate that that genus 
is by no means so abundantly represented in other parts of the world as it is on the 
north-western coasts of Europe. 
Sarcobotrylloides and Polycyclus occur in the “ Porcupine ” collection, but all the 
Challenger Botryllidse belong to the genus Botrylloides in the restricted sense. On the 
^ He calls them subgenera, but treats them as genera. 
