This paper gives a detailed description of the digestive and reproductive systems of the New Zealand land operculate Murdochia pallidum (Family Cyclophoridae), with a discussion on the morphological changes involved in the transition from the sea to a land habitat The Cyclophoridae have accomplished the transition from the sea to a land habitat with relatively few modifications of their primitive structure.

The Cyclophoridae represent one of several groups of terrestrial molluscs that have evolved from the marine gastropods belonging to the Sub-class Prosobranchiata. They are wholly distinct from the later-derived pulmonate stock, remaining much more generalised in the structure of the animal, and being conveniently referred to collectively as the “land operculates.” Three such families are represented in the New Zealand fauna, the Hydrocenidae, which originated among the Neritacea; the Cyclophoridae; and the Realiidae. The two last-named families are generally held to have arisen from littorinid-like marine ancestors; they are probably only distantly related, though by Thiele (1935) the two groups, together with a long list of other terrestrial mesogastropods are loosely associated in the Stirps Archaeotaenioglossa. Of the structure of the Cyclophoridae we have little detailed knowledge, although from Bouvier's picture (1882) of the nervous system of Cyclophorus tigrinus, with persistent ladder-like pedal ganglionic cords, it has long been inferred that they are highly primitive among mesogastropods The New Zealand members of the Cyclophoridae belong to the genus Murdochia, and are all of small size, seldom exceeding 5 mm. in length. The family has a wide distribution in S. E. Asia and the East Indies, Central America and the West Indies; some of the tropical species are of temptingly large size, and would be especially suitable for the detailed work on living gut and genitalia, which will be required before a confident assessment of the group is able to be made. But in view of the present lack of anatomical work, and the interest of the genus Murdochia among neozelanic land mollusca, it was felt that the following observations would prove of some value. It is hoped in a later paper to expand the present account, especially as regards reproductive activities, and also to provide a description of the New Zealand genera Hydrocena and Realia.

Material of Murdochia pallidum was dissected alive after removal of the shell, fixed in Bouin's and dissected preserved, also sectioned at 8μ and stained in Delafield's haematoxylin and Van Giesen's picrofuchsin. Mr. C. B. Trevarthen kindly collected several batches of living Murdochia, and his assistance is gratefully acknowledged. The writer is also indebted to Dr. W. D. Reid, of the Plant Diseases Division, D.S.I.R., Owairaka, Auckland, for carrying out a culture trial with the spirochaetes from the stomach.

branchial gland extending along the right side of the pallial roof, unaltered in histological structure from that of marine prosobranchs; and a narrow zone of sub-epithelial gland cells encircling the mantle just within its margin; these probably serve to seal the closed operculum, during prolonged withdrawal of the animal into the shell. The colour of the exposed parts of the head and foot is greyish-black, and the head, snout and short, paired tentacles are jet black. The pallial wall is divided into regions, the respiratory area occupying the left half, the hypobranchial gland to the right, and behind it the yellowish renal sac. The visceral mass is largely occupied by the digestive gland, composed of a mass of stout reddish-brown lobules, investing the stomach, which is seen from the surface as a translucent white sac. The gonad is quite large, forming a spacious undivided sac, applied to the convex surface of the digestive gland. It is white in the male, deep yellow in the female.