Before describing the section at Limpley Stoke I wish to acknowledge the very kind help given to me by Dr. W. D. Lang, F.R.S., Keeper of the Department of Geology in the British Museum (Natural History), who has had the fossils examined and through whose encouragement I am recording the results of an investigation extending over a considerable time.

The following observations are the result of working over the Middle Jurassic Arcidae with a view to monographic treatment of the Corallian and Bathonian species. The monographs must of necessity be slow in appearing, and in any case they are not the place to discuss the broader conclusions to which the investigations have led. The family is one full of interest from an evolutionary point of view, but an exceptionally involved maze of controversial matter, chiefly concerning nomenclature, by which the Arcidae have been burdened, has obscured the features of interest and the phylogeny.

The Farsan Islands form a group in the southern part of the Red Sea, about 17° N. Lat., 42° E. Long., and lie some 40 km. off the Asir Coast of south-west Arabia. The two main islands are Farsan Kebir (whose north-western arm is known as Seïr), and Segíd, which nestle together with a length of 60 km. and breadth of roughly 25 km. There are five smaller islands varying in length from 5 to 13 km., and a host of minor islets and rocks. The islands are in general of rather low elevation, not rising to more than 10 to 20 metres above sea-level. Local hills occur up to 75 metres, and are mostly due to faulting, occasionally to folding.

The material which is described in this note was collected by members of the Geological Staff of the Anglo-Persian Oil Company, Ltd.