1. The occurrence of an Enteropneust in Wales is described, and an account given of the environment.
2. Saccoglossus cambrensis, sp. n., is distinguished by the following characters:-
Coloration; relative proportion of proboscis and collar; dorsal groove running the whole length of the proboscis, with a well-marked nervous thickening beneath; large number of gill-slits (80–90 pairs); gonads beginning a t the middle of the branchial region; absence of genital ridges; absence of projecting ridges formed by the ventral longitudinal muscle bands of the trunk; four to six concentric rings distinguishable in the arrangement of the longitudinal musculature of the proboscis; large pericardium; absence of a dorsal glomerulus; proboscis skeleton not reaching beyond the middle of the collar, and little more than half-way round the buccal cavity; five epidermal zones in the collar; complete separation of right and left collar cavities; absence of a dorsal pouch of the buccal cavity; discontinuity between the tissues of the nerve cord and the epidermis of the collar, except at the ends; collar-trunk septum deflected forwards to the middle of the collar; marked ciliation of the epidermis covering the ventral nerve cord in the intestinal region; shallow ventral pharynx; broad tongues, projecting more than the septa; histological details of the oesophagus; eight to twelve intestinal pores, of which the first three to five are rudimentary; simple unlobed gonads, large size of ova, and presence of yolk-cells in the ovaries.
We are greatly indebted to Professor W. M. Tattersall and to Professor C. J. van der Horst for much advice, and to the former for specimens of S. ruber. We wish to take this opportunity of expressing our thanks also to Professor J. P. Hill, F.R.S., for his advice and interest in the work; to Professor G. W. Robinson for preparing the analyses of soil given in Appendix I.; to Mr. L. H. Jackson for assistance in various ways, and to Mrs. Jackson for the drawing reproduced in PI. I.