MARSHAL!. : ADDITION'S TO "BRITISH CONCHOI.OOV." 67 



continuous. It is scarce, but more plentiful and larger at Scilly than 

 elsewhere, whence Mr. Clifford Burkill has taken as many as 40 in a 

 tide, and six under one stone. 



Nudibranchiata Cuv. — The nudibranchiate moUusca have under- 

 gone much investigation, and a great deal has been written on the 

 subject, since "British Conchology" was published, while even what 

 that work contains is admittedly only a compilation of Alder and 

 Hancock's researches, published more than a decade previously. 

 Canon Norman, than whom no British writer is better qualified to 

 deal with this family, brought it up to date and published it in the 

 "Annals" for 1890, vols. v. and vi. 



Assiminea grayana Leach. — The habitat for this species given 

 by Jeffreys, " Banks of the Thames between Greenwich and a little 

 below Gravesend,"^ though nearly correct when his work was written, 

 has undergone considerable change in the interval. Previous to that 

 time Dr. Gray, Mr. Clark, and others found it abundantly between 

 Greenwich and Woolwich, but when Gwyn Jeffreys wanted living 

 specimens to illustrate his work, he could find only two specimens 

 after the most diligent search, assisted by myself. Subsequently, 

 however, I found them in great numbers at Abbey Wood and Erith, 

 lower down but on the same side of the Thames, and as this is now 

 its nearest locality to London, it would appear to have migrated for 

 about ten miles towards the sea. During the same interval a near 

 neighbour of this species, Hydrobia similis, has almost disappeared 

 from the same district, where it was common 30 years ago, and H. 

 jenkinsi has arrived to supplant it. Mr. J. E. Cooper mentions it 

 from Sandwich, and also as living " in abundance on the banks of the 

 Blyth near Blythburgh," while Mr. Mayfield has recorded "a few 

 examples" from the rejectamenta of the river Aide in Suffolk, and 

 there are several other records cited by him, some of which at least 

 require confirmation. It may easily be mistaken for one of the many 

 forms of Hydrobia jtlvcB. 



A variety has a narrower and rounded base, with a deeper suture. 

 Jeffreys' figure exhibits an umbilicus, which is incorrect; but his 

 generic figure is right in this respect. In Sowerby's the mouth is 

 much too large, besides being wrongly shaped, and neither figures are 

 sufficiently conical, 



A. littorina Del. Ch. — Caldy Island (Williams -Vaughan) ! 

 Guernsey, Sennen Cove and the Lizards, Torbay and Dartmouth, 

 Portland Island. An Alderney record by Mr. Marquand is not this, 

 but a minute form of Littorina rudis var. saxatilis. 



I Brit. Cough., vol. v., p. loo; 



