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IN a previous letter announcing the discovery of the barnacle Chthamalus stellatus in the Isle of Man, it was pointed out that large areas of the Irish Sea coasts had never been investigated1. A complete investigation was begun after finding Chthamalus at Portpatrick, Galloway, in November 1949. The investigation has recently been completed, and it is possible both to confirm and amplify the recent records of Crisp2 and Williams3.

THE barnacle Chthamalus stellatus Poli is found on the shores of the British Isles west of a line running from Dunnet Head (Caithness) to Swanage in Dorset. It penetrates the Irish Sea northwards as far as Dublin and Anglesea, but is reported as absent from the Isle of Man, as well as from the eastern part of the English Channel and from the North Sea coast1. Its occurrence appeared to be connected, in some unknown way, with Atlantic as opposed to North Sea water1. It is, however, possible to suggest tentatively a simple explanation.

RECENT suggestions have been made relating the distribution of Chthamalus stellatus1,2 to low-temperature isotherms. It may therefore be of value to put on record some new observations on its breeding made over the past three years, which have a bearing on present distribution.

IN the course of a quantitative survey of the Manx intertidal zone, the high-water barnacle, Chthamalus stellatus Poli, was discovered at Port St. Mary and has since been found to be generally distributed around the island. The rediscovery has been thought worth recording in view of the apparent conflict between previous accounts for the area (present: Darwin, 18541, Marrat, 1886 2; absent: Moore and Kitching (1934), 1939 3), and because of the great interest in the species in its more sparse localities.

IN previous communications1,2 the possibility that changes may occur in the distribution of intertidal organisms over a number of years was discussed, and the established distribution of Chthamalus stellatus was extended to include much of the Irish Sea coastline. Further new evidence has come to light showing that while this barnacle may have increased its range and abundance over recent years, it was nevertheless present in the Isle of Man in 1933. A photograph taken by H. B. Moore in March 1933 shows a single individual which appears on close inspection to be Chthamalus ; moreover, statistical tests based on the size and form of the aperture and the angle of the scutotergal margin show that this must be Chthamalus and not Balanus balanoides.

IN a paper discussing the distribution of Chthamalus stellatus in British waters, H. B. Moore and J. A. Kitching1 attempted to link up the distribution of this barnacle with that of Atlantic water. Recently, Kitching2 suggests that air temperature may be the limiting factor, abandoning to some extent the Atlantic water theory, but adding “although from the known facts the latter is equally possible”. Southward3 has recently recorded the general occurrence of Chthamalus in the Isle of Man, and he too points out that there appears to be some correlation between air temperature and the distribution of the species. In the map of Moore and Kitching, Chthamalus is unrecorded between Howth and Belfast Lough and given as absent from the east coast of Antrim but as present at Portstewart on the north coast. It was also recorded as absent from the Isle of Man.

IT was originally suggested by Darwin1 that the susceptibility to disintegration of the shell of the common littoral barnacle, Chthamalus stellatus (Poli), was a consequence of its high content of organic matter. This suggestion has been accepted by many authors ; but there appears to be no analysis to support the contention.