232 NOTES ON THE MOLLUSCA OF THE THAMES ESTUARY. 



No doubt, owing to its extreme minuteness, and its habit of hiding 

 among moss, it is frequently overlooked. 



//. — Brackish Water Shells (^generally classed as Marine) inhabiting 

 the Alarshes of the Thames Estuary in Kent and Essex. 



Order PECTINIBRANCHIATA. 



Family LITTORINID.E. 



Littorina rudis, Maton. Small brackish water variety ; asso- 

 ciated with Hydrobia ventrosa, and Assiniinia grayana. Ditches 

 upon East Tilbury Marsh. 



Hydrobia ulvae, Pennant. Grays, Tilbury, Greenhithe, and 

 Gravesend. 



H. ventrosa, Montagu. From Erith to below Gravesend, 

 Kent ; Coldharbour Point to below Tilbury Fort, Essex. 



H. similis, Draparnaud. Erith Marshes ; one dead shell at 

 Beckton ; two live and one dead shell, marshes near Abbey ^^'ood, 

 1890. 



Var. Candida^ Jeff. Occurs sparingly with type. (A clear 

 pellucid variety.) 

 H. jenkinsi, Smith. The most abundant shell of this genus 

 upon the Thames Marshes ; from the commencement of Plumstead 

 Marshes nearly to Northfleet, in Kent, and from Beckton to Cold- 

 harbour Point, Essex. 



Var. ecarinata, Jenkins. Shell smooth, without keel or 



tufts ; occurs with type. 

 Var. tiimida, Jenkins. Shell much inflated, very short spire ; 



ditch near Beckton. 

 Var. gracilis, Jenkins. Ditches; Rainham and Erith Marshes 



Order PULMONOBRANCHIATA. 



Family ASSIMINEDM. 



Assiminea grayana, Leach. Between Coldharbour Point 

 and Purfleet ; also from Grays, extending some distance down the 

 river below Tilbury Fort ; and in Kent from Greenhithe to below 

 Gravesend ; abounding in the canal near the latter place. 



Fami LY CAR \ XHIID. E. 

 Melampus myosotis, Drap. Associated with Assiminea in 

 the same localities. 



