PLYMOUTH MARINE INVERTEBRATE FAUNA. 161 



and Eulalia viridis. The overhanging ledges of rock give shelter to 

 colonies of encrusting sponges {Hymeniacidoii sanguineum, Halichondria 

 panicca, and Syconcomprcssum), compound Ascidians {Botryllus violaccus, 

 BotryUoides ruhrnm), and Polyzoa {Umhonula verrucosa, Crisia), upon, 

 Vi^hich Xudibranchs {Arcliidoris tuhcrculata, ^olidia jMpillosa) feed. 



On the Fucns the Hydroid Serlidaria pumila, the Polyzoa FlustrcUa 

 hispida and Mcmhranipora pilosa, and Spirorbis horealis occur in quan- 

 tity, and, on the Laminaria, Memhranipora memhranacea in large patches. 

 Clava squamata and Coripie var/mata are also often plentiful. 



The cracks and crevices between the layers of shale shelter a 

 characteristic and typical fauna, of which Terchclla lapidaria, Am- 

 phitrite gracilis, Polydora jiava, Fotamilla reni/orviis, and Petalostoma 

 minutum are representative species of the higher and intermediate tidal 

 zones, whilst Marphysa sanguinea and Polymnia nehidosa occupy a 

 similar situation near low-water mark. 



The patches of gravel and coarse sand contain at the higher tidal 

 levels Audouinia tciitacidata in large numbers, and the intermediate 

 and lower zones are characterised by the presence of large Kcphthys 

 cceca, Sthenelais boa, Nereis cultrifera, and Glycera convoluta. 



Patches of fine sand, the most productive of which lies immediately 

 south of Batten Castle, are found to contain Arenicola marina, Lanice 

 conchilega (in sheltered situations near rocks), JSfephthys twca and JV. 

 Hombergi, Pectinaria Koreni, Scoloplos armigcr, Magclona papillicomis, 

 Pmcilochmtus serpens, Scolelcpis vulgaris (in black muddy sand), and a 

 number of other sand-burrowing Polychsetes, the burrowing brittle star 

 Ophiocnida brachiata, and the Lamellibranclis Ctdtellus pellucidus and 

 Tapes pullastra. 



On stony ground the following species are met with in considerable 

 abundance beneath the stones: Gammarus marinus, PorccUana platy- 

 cheles, Cancer pagurus, Garcinus mcenas, Porhmus indter, Nchalia bipes, 

 Galathca squamifera, Lepidonotus clava and L. squamata, Anqjhiura 

 elegans, Asterina gibbosa, Ophiothrix fragilis, Leptoplana. tremellaris, 

 Botryllus violaceus. Actinia equina, and during the winter months 

 Goniodoris nodosa. 



At the western end of Rum Bay, under Batten Castle, the shale joins 

 the Plymouth limestone, and there is a mass of high rocks of the 

 latter kind, with a fauna similar to that described in a subsequent 

 paragraph. 



Drake's Island and Mount Edgcumbe. From their position off 

 the UKuith of the Hamoaze Estuary, the shores of Drake's Island and 

 Mount Edgcumbe are under the inllueuce of tidal streams of consider- 

 able force, whilst at the same time they are sheltered from the south- 

 west, and hence not exposed to the most violent wave action. The 



