162 TLYMOUTH MARINE INVERTEBKATE FAUNA. 



shores of Drake's Island are for the most part rocky, the rocks, com- 

 posed of a hard grit, being generally steep and high. Between the 

 rocks are small patches of stony ground, and of sand and gravels of 

 various textures. The shores of Mount Edgcumbe resemble the stony 

 patches on Drake's Island, and may be treated with them. 



The fauna on the rock faces resembles that at Eum Bay, and needs 

 no further detailed description beyond a notice of the fact that owing 

 to the steeper character of the shore and the height of the rocks, the 

 extent of surface exposed at each of the tidal levels becomes very much 

 reduced, so that those animals which are restricted to a particular zone 

 are represented by a relatively snuiUer number of individuals. 



The overhanging ledges of rock are larger and more profusely covered 

 than those at Hum Bay, but the same species are plentiful. Perhaps 

 the most important addition to be made to the list given for Kum Bay 

 is the Ascidian Clavelina lepadiformis, which during some summers has 

 been very abundant beneath these ledges. 



The characteristic fauna in the crevices of the soft shale at Eum Bay 

 is not so marked at Drake's Island, though Marphysa sanguinea and 

 Polymnia nehulosa are plentiful in crevices at dead low water. 



On stony ground between the rocks at Drake's Island and along the 

 Mount Edgcumbe shore, in addition to the species found under similar 

 circumstances at Rum Bay, there may be found beneath the stones, 

 more plentifully than at the latter locality, specimens of Cucumaria 

 saxicola, Cucumaria Normani, and Echinus miliaris, whilst 3l//riothcla 

 2)hri/gia is very frequent attached to the under surface of the stones. 



On the south side of Drake's Island a patch of clean shell gravel 

 is exposed, which is probably continuous with the shell gravel of 

 Queen's Ground (cf. p. 165). In addition to numerous specimens of 

 Carcinus mcenas, which are often of variegated colours matching the 

 colour of the shell gravel, the crab Pirimela is found, whilst in the 

 gravel Glycera gigantea occurs. 



On the north-east side is a patch of sand, which is the most 

 characteristic bit of clean, even-grained sand in the district. Its 

 fauna includes Ammudytes, Natica Alderi, and Spisida {Mactra) solida. 



A Zostera-hed exposed on the north side of the Island contains 

 numerous Solen, occasional specimens of JEchiiwccoxlium , whilst a patch 

 of a few square yards of harder sand is crowded with Lutraria elliptica. 



Limestone Shores (Rocks below Laboratory and under West 

 Hoe ; Rocks at Batten). The rocks on the limestone shores differ 

 from the shale rocks which have been described at Rum Bay, in being 

 much higher, in forming a large number of rock pools at the higher 

 tidal levels, and in ])eing of a much harder and closer texture, with few 

 cracks and crevices. The rock fauna at the higher tidal levels, there- 



