[None. Introduction as follows:]
The Annelids here described were collected by Mr. W. F. Purcell in the years 1896 and 1900, with the co-operation of Messrs. G. H. Glasson and R. M. Lightfoot. The collection was sent, by arrangement, from the South African Museum to the British (Natural History) Museum, and intrusted to me for examination. Most of the specimens were preserved in an alcoholic solution of corrosive sublimate, and, in many cases, care had been taken to procure the extrusion of the proboscides, which is a matter of importance in the systematic study of errant Annelids.
There is a pronounced Mediterranean and Northern element in the Annelid fauna of the Cape, a feature which has already been noted by Dr. von Marenzeller, and, indeed, it would appear that the geographical distribution of marine Annelids is primarily determined by thermal considerations. Many species are eurythermal, and hence cosmopolitan or pan-oceanic; where this is not the case, we frequently meet with instances of discontinuous distribution, the areas of distribution being separated by thermal barriers. The only terrestrial barriers of first importance are the Isthmus of Suez and the Isthmus of Panama, and that these have not always prevented the inter-oceanic exchange of types is clear from the fact that the Annelid fauna of the Indo-Pacific region may be said to be composed of an assemblage of endemic, Caribbean, and Mediterranean constituents.