190 6- 1907.] Copcpoda living as Messmates with Ascidians. 361 



The Copepoda I now proceed briefly to describe may be 

 arranged as follows : — 



A. NOTODELPHYOIDA Sars. 



1. Females provided with a single dorsal incubatory pouch in place of 

 external ovisacs : — 



Notodelphys Allman. Doroixys Kerschner. 



Agnathaner Canu. Bonnierilla Canu. 



Doropygv.s Thorell. Gunenotophoms O. G. Costa. 



Notopteropkorus O. G. Costa. Botachus Thorell. 



2. Ovisacs, two, external, situated on the dorsal aspect, contiguous, and 

 comparatively small, or situated laterally and more or less elongated : — 



Ascidicola Thorell. Enteropsis Aurivillius. 



. Botryllophilus Hesse. Aplostoma Canu. 



Enterocola P. J. van Beneden. 



B. CYCLOPOIDA. 



Lichomolgus Thorell. 



In Lichomolgus the fourth pair of swimming - feet has the outer 

 branches three- jointed, but the inner only two-jointed, and this forms 

 one of the principal points of difference between it and other genera 

 of the Lichomolgidse. In Pseudanthessius, for example, the inner 

 branches of the fourth pair consist of only one joint, while in 

 Herrinannella they are three-jointed like the outer branches. 



I shall now proceed to make a few observations on the 

 better known species belonging to the various genera men- 

 tioned, and in the order in which they are given. 



Genus Notodelphys. 



Four species of Notodelphys have been recorded for the 

 British Islands — viz., Notodelphys Allmani, N. ccerulea, JY. 

 agilis, and N. prasina. These have all been described by 

 M. Thorell. The first - named appears to be the most 

 common. I have obtained it in the Firth of Forth, in 

 Loch Tarbert, and at Tarbert Bank at the mouth of Loch 

 Fvne : indeed, whenever large and aged Ascidians are brought 

 up in the dredge or trawl-net we nearly always find these 

 Copepoda in the branchial chamber, and frequently other 



