MOLLUSCA. 61 



shores being absent. A worn valve oi Isocardia cor found dii 

 the West Sands is purely accidental. Tdlina pusilla and 

 Psammohia telUnella are uncommon at St. Andrews. Amongst 

 univalves, TricJiotrojns horealis, Pleurotoma Trevelyana, 

 Aplysia punctata, and Philine pruinosa are notevvortliy. 

 Tlie smaller univalves, such as Rissoce and their allies, are 

 much less numerous in species than on the southern and west- 

 ern shores, the absence of Trochus umbilicatus being especially 

 diagnostic when contrasted with the latter. The Nudibvanclis 

 are well represented at all seasons ; and the individuals in the 

 majority of the species are numerous. Ommatostrephes and 

 Loligo amongst the cuttles often occur in great profusion on 

 the West Sands after storms. 



On the whole the species are northern, and stand in strong 

 contrast to the molluscan fauna of the western shores, where 

 Thracia convexa, Tapes decussatus, Pecten vari'us^ var. nivea, 

 Teredo megotara and T. norvegica, Fissurella, Trochus umhili- 

 catus and T. zizypliinus in the littoral zone, and the abund- 

 ance of T. magus and T. tumidus in the laminarian, Phasianella, 

 Alcera buUata, Eli/sia, swarms of large and small Rissoce, and 

 the pelagic lanthina form conspicuous features of the marine 

 fauna, just as the hosts oi' Bulinjus acutus do on the sandy 

 fields of Killipheder and other parts of the extreme west. 

 Still more evident is the contrast with the rich southern species 

 that cluster round the Channel Islands— such as the finely 

 developed pectens, oysters, and Anomice, and the appearance of 

 the former between tide-marks (P. varius), besides Mytilus 

 harhatus (which takes tlie place of the bearded varieties of our 

 Mytilus modioTus) in obscure crevices in the littoral zone, the 

 frequency of Area tetragona in fissures of the rocks, Galeomma 

 on the under surface of stones in tide-pools at Herm, the boring 

 Gastrochrenam shells, and the abundance oi Haliot is. Pandora, 

 Venus verrucosa and V. ovata, Mactra glauca, the Psammohia', 

 and the "angel's wings" {Lima), which when disturbed flit 

 with their brilliant orange fringes so nimbly in the tide-pools. 

 Amongst univalves, again, the large size and abundance of 

 Chiton discrepans, Fissurella, Emarginida, Murex erinaceus, 

 Aplysia jmnctata, Euli7na j}olita, Trochus Itneatus, Cerithium 

 and Gerithiopsis, and the predatory and cunning cuttles 



