166 PLYMOUTH MARINE INVERTEBRATE FAUNA. 



overboard there, and many of the species from outside amongst this 

 refuse are capable of surviving for a time. 



THE YEALM ESTUARY. 



In the Yealm Estuary is a large body of enclosed and sheltered water, 

 with a fauna which is essentially marine for a considerable distance 

 above tlie mouth. The mouth is almost closed by a bar of sand, a 

 deep channel being left only on the southern side. At a distance of 

 about a mile from the mouth, the estuary divides into two branches, 

 the Yealm Eiver proper and Newton Creek. The Y'ealm possesses a 

 number of rich collecting grounds, which would well repay a more 

 careful and detailed study than they have yet received. 



Shores. 



Yealm Sand - bank. This name has been used in the records to 

 indicate a bank of fine to medium sand on the left bank of the Yealm 

 Kiver above the junction with Newton Creek, which is uncovered at 

 low spring tides. The fauna is characterised by the presence in the 

 sand of large numbers of Unsis ensis. By digging may also be obtained 

 in more or less considerable numbers Synapta inhcerens, Tapes jJuJlastra 

 and T. decussatus, Sjnsida solida, Gari deprcssa, Sigalion hoa, Amphitrite 

 gracilis, and large specimens of Nephthys cara. On the surface of the 

 bank are found Calliostoma zizyphinus, and, during the summer months, 

 Aplysia punctata, both in considerable quantities. 



Eastern Shore below junction of Yealm River and Newton 

 Creek. Along this shore tlie soil is composed of a coarse, muddy 

 gravel, the most striking feature of the fauna of which is the abund- 

 ance of tlie large Terebellid Amphitrite Johnstoni, with its commensal 

 Polynoid, Onftyana cirrosa. Sealihregina inflatuvi is also found here. 



Zostera Bed near the Mouth of the Yealm. Along the southern 

 shore a Zodcra bed is just exposed close to the mouth of the estuary. 

 The muddy sand in which the Zostera is rooted contains an abundant 

 Polychiete fauna, of which the two most numerous species are Aonides 

 oxycephala and Marphysa Belli, whilst Notomastus rubicundus and N. 

 latericeus are also found. 



Dredging and Trawling Grounds. 



The channel of the river just below the junction of the Yealm and 

 Newton Creek is the best dredging ground in the estuary. The bottom 

 is covered with stones and shells (chiefly oyster-shells), to which red 

 and brown seaweeds are attached in considerable quantities. Echiyius 



