PLYMOUTH MARINE INVERTEBRATE FAUNA. 163 



fore, shows special features on the limestone shores, whilst the fauna 

 characteristic of the cracks and crevices between the layers of the 

 shale is not represented. The upper portions of the rocks are densely 

 covered with barnacles, amongst which the molluscs Otina otis and 

 Leuconia hidentata are plentiful. Tlie sides of the rock pools are 

 covered by growths of Coralline, red and green seaweeds, Hydroids 

 such as Syncoryne gravata, Clava squamata, small Tuhidaria, and the 

 sponges Leucosolenia hotryoides, L. coriijjlicata , L. variabilis, and Clath- 

 rina coriacea. In certain of these pools the Archiannelid Dinophilus 

 tceniatus is found in great numbers. Saxicava rugosa and Cliona celata 

 are abundant, boring in the limestone. 



In other respects the fauna on the limestone rocks does not greatly 

 differ from that on the shale, the free-living animals being almost 

 exactly the same. Some of the overhanging ledges are densely covered 

 with the Ascidian, Styelopsis grossidaria and Fotamilla reniformis is 

 very abundant. 



The Breakwater. The most interesting feature of the fauna of the 

 Breakwater is the collection of animals which are found boring in the 

 limestone of which it is built. To such an extent is llie stone eaten 

 into by various animals that considerable damage is done to the struc- 

 ture, and constant repairs are called for. In a stone which has been 

 injured through this cause the outer surface, to the depth of about 

 a quarter of an inch, is converted into a honey-combed, friable mass 

 through the ravages of the boring sponge Cliotui celata, whilst at fre- 

 quent intervals larger holes, each of which may have a diameter of a 

 quarter of an inch, and may pierce the stone to the depth of one inch, 

 are formed by the boring mollusc, Saxicava rugosa. To these two 

 animals most of the damage is due, but in addition there are found a 

 few holes formed by the mollusc Gastrochcena diibia, and many by the 

 Polychictes Dodecaccria concharum, Polydora ciliata, rolydora hop- 

 lura, and Fotamilla reniformis (the Sahella saxicava of Quatrefages). 

 Dodecaceria forms holes of oval or figure of eight section, which may 

 penetrate for a depth of several inches into the heart of the stone ; 

 Polydora ciliata forms small U-shaped burrows, open at each end, 

 whilst F. hoplura makes similar burrows of larger size.* 



Other features of the fauna of the Breakwater are the abundance of 

 the anemone Corynactis viridis, and of a small salmon-red anemone at 

 present undescribed, of Caryopkyllia Smithi and of Gcdathea strigosa. 

 Large nests of Lima hians have also been found there. 



* The facts here recorded were investigated at the request of tlie Government 

 engineers responsible for the repair of the Breakwater, and a n-port was furnislied 

 on the suV)ject. — E. J. A. 



