Scilly is composed of some three hundred islands and rocks, and lies 28 miles off Land's End in a westerly direction. Only five of the Islands are inhabited and the largest of these, St. Mary's, is no more than nine miles in circumference. These Islands are therefore ideal grounds for the Marine Biologist. For some years I have been fortunate in being able to join in a residential Field Course on these Islands. The number of students varies between 20 and 30 and their ages from 13 to 60; their interests range through Geology, Ornithology, Entomology, Botany, Marine Biology and Conchology; at home they may be housewives, engine-drivers, head-mistresses, professional biologists or senior pupils. All are encouraged to collect and report on specimens for one another whatever their interests. Twice a day they meet to identify and discuss specimens.
The Scillies lie exposed to winds from all quarters. The climate is mild as is witnessed by the sub-tropical gardens on the Isle of Tresco, but the sea is rarely calm and the waves constantly batter the granite shores. Most of the species of the Cornish coast are common to the Scilly Isles. In the Victoria County History of Cornwall (1906) Scilly had some 280 species compared with about 350 in the Cornish records. Many of the species not present in the Scillies (compared with Cornwall) are rarities, but there are some note-T/orthy absentees.
None of the rock-boring Piddocks occur as they are presumably unable to make niches in the famous Scilly granite which contains much quartz. Dwarfed specimens of the rock-borers Hiatella gallicana. (Lamarck) and H. arctica (Lamarck) occur in small numbers in the hold-fasts of sea weeds, though it may be noted that the inter-tidal brown fucoids are rare on these exposed shores. Two of the commonest species on Cornish rocky shores are absent from Scilly. One is the mussel of which only a few solitary specimens are to be founds they are very incurved forms, probably of the Mediterranean species, Mytilus galloprovincalis Lam., which is commoner than the Common Mussel, M, edulis L., in most parts of Cornwall. The other is the Edible Winkle, Littorina littorea (L.) of which only two specimens have ever been recorded.
The Scillonians eat Thick Top shells, Monodonta lineata (da Costa) which they call Winkles, and which are both abundant and of a great size on most of the shores. Small 'kitchen-middens' of these shells may be seen used as rut- fillings on some of the rough roads of St. Martins. Least Winkles, Littorina neritoides petraea (Mont. 1803), and Rough Winkles, Littorina saxatilis (Olivi), are found wherever there are suitable cracks and crevices, but nowhere are they common -the commonest subspecies of the Rough Winkle are Littorina saxatilis rudis (Maton) and Littorina saxatilis nigrolineata Gray, the latter reaching well over half an inch in length.
Patella depressa Pennant and Patella vulgata L., are equally common, but Patella athletica Bean, typical of exposed shores on S.W. coasts seems to be quite sparsely distributed in these islands. On the south shore of Tean which was notably more sheltered than other shores visited, P. depressa was not found, and P. vulgata was large and plentiful.
Purple Dog Whelks, Nassarius reticulatus (L.) are common, but nowhere abundant, perhaps because mussels, their main food elsewhere, are so rare.
Many of the mollusca v/hich on sheltered shores would be found amongst the sea-weed fronds, seek shelter under the thousands of blocks and boulders, often of enormous size, which are strewn or banked up on most of the shore line. Flat Tops, Gibbula umbilicalis (da Costa) and Grey Tops, G. cineraria (L.) are abundant under many of these boulders. Some years enormous Plumed Sea Slugs, Aeolidia papillosa (L.) are to be found in the Spring, spawning prolifically.
Amongst the smaller shells Cingula semistriata (Mont.), Cingula cingillus (Mont.), Rissoa parva (da Costa) and its variety interrupta are very common. Lasaea rubra (Mont.)is fairly common and last year some specimens of Kellia suborbicularis (Mont.) were found. This year we had our first tentative attempt at dredging and took dozens of Small Spire shells, Rissoa parva (da Costa). These were bright pink with encrustations of the tiny coralline alga, Melobesia sp.J they looked very beautiful as the tiny snails moved along the leaves of the Eel grass on which they were found.
Mrs. S. M. Turk