8 



BA RD WICKE'S SCIENCE- G OSSIF. 



little stiffened, as might reasonably enough be expected 

 from the heat imparted to them from the bodies of 

 the birds during the process of the second lining of 

 the nest and the egg-laying, combined with the 

 dryness of their situation. This double lauter of 

 eggs was probably due to the death, by accident or 

 natural causes, of the first female owner of the nest, 

 and her partner's taking a second mate who had 

 commenced housekeeping on her own account by 

 having a second lining added to the nest upon which 

 to deposit her own incipient offspring. 



Sand martin (Cotile rijiaria).— On }\mQ ^ih, 1885, 

 I took from its deep burrow in the bank of the 

 stream Blythe, a nest of the sand martin which 

 contained four eggs unincubated, and which was 

 composed of dry grass and grass-stems, and lined 

 with soft fowl feathers and a little dry grass. This 

 nest, like that of the swallow described above, was a 

 double one ; for beneath this upper lining upon 

 which rested the four eggs, was a second (a former) 

 lining of fowl feathers, upon which lay two other 

 eggs quite fresh though very dirty. Here, too, in all 

 probability, some fatality had overtaken the original 

 female owner of the nest after she had deposited two 

 of her eggs ; and her partner had then found a second 

 mate, whose nearly completed lauter the upper four 

 eggs would be. The sand martin lays from five to 

 six purely white eggs, which, however, are generally 

 more or less soiled and abundantly speckled with the 

 dark-green excreta of the large fleas (Pulex) with 

 which their nests almost invariably swarm. 



Charles Robson. 



NOTES CONCERNING THE DISTRIBU- 

 TION OF MOLLUSCA IN THE THAMES 

 ESTUARY. 

 By A. J. Jenkins and L. O. Grocock. 



SINCE the publication of the article upon "The 

 Distribution and Habits of the British Hydro- 

 bias," Science-Gossip, 1890, page 103, it has been 

 our endeavour to try our best to work up the distri- 

 bution of the various other species of mollusca in- 

 habiting the marshes of the Thames Estuary, with a 

 view to studying the habits and localisation of the 

 brackish-water species in particular, as well as the 

 discovery of the distribution and true limits of the 

 HydrobitC and allied forms to be found in close 

 proximity to the river. 



All the British I lydrobioe have been taken from the 

 Thames marshes, and the two species, Hydrobia 

 similis, Drap., and H. Jenldnsi, Smith, have not up 

 to the present been found elsewhere in Britain. 



The district which we decided to investigate is 

 included between the commencement of the Plum- 

 stead Marshes, near Woolwich Arsenal, and North 

 Woolwich, upon the Essex bank of the Thames, down 

 to a point three miles below the forts at Tilbury and 

 Gravesend. 



Nearly twelve months have elapsed since we com- 



menced working this district in a systematic manner,, 

 and during this period the course of the Thames has 

 been followed from Woolwich to below Gravesend, 

 and many excursions have been made to the other 

 side at North Woolwich, Beckton, Coldharbour 

 Point to Purfleet, and over the marshes at Grays, 

 Thurrock, and Tilbury. During these excursions we 

 have indulged our prying propensities to the best of 

 our ability, using our dredges freely over many miles 

 of ditches of fresh and brackish water, at the same 

 time keeping a sharp look-out for terrestrial forms 

 either possessed of shells or destitute of them ; care- 

 fully recording each day's experience gained, and 

 taking notes of fresh captures. 



We have also received much valuable assistance^ 

 and have occasionally been accompanied in our expe- 

 ditions by the Rev. J. W. Horsley, the indefatigable 

 President and Founder of the now flourishing Wool- 

 wich District Natural History Society, which under 

 the guidance of Mr. Horsley has organised a series of 

 Saturday half-holiday field-excursions for the study of 

 the fauna and flora of the district. 



The marshes bordering the Thames are very ex- 

 tensive, and a considerable portion is devoted to 

 market-gardening and grazing purposes, a large area 

 still remaining almost in its original pristine condition. 

 The great national workshop, Woolwich Arsenal, is 

 built upon the Plumstead Marshes, and a range, 

 fifteen hundred yards in length, is devoted to gun- 

 practice near the Arsenal. Many chemical and 

 manure works are also built upon them. At Purfleet 

 there is a rather extensive salt-marsh. 



Lying, as they do, considerably below high-water 

 mark, the marshes were many years ago protected 

 by a river-wall or earthwork. The origin of this 

 gigantic earthwork, which confines the Thames to its 

 present channel, is lost in obscurity, but probably 

 various portions have been constructed at different 

 periods. Intersecting the marshes in various direc- 

 tions are numerous dykes or ditches, which abound 

 in the various forms of life which delight the eye and 

 mind of the biologist, conchologist, and microscopist. 



In places near the river the ditches are connected with 

 the Thames by drains and sluices, and such ditches 

 being liable to the overflow of the river occasionally, 

 at high tides, causes the water contained therein to 

 be more or less brackish. These ditches form the 

 habitat of our Hydrobice and their alhes. A long 

 walk across the marshes in fine weather is very 

 exhilarating and enjoyable ; after fogs and heavy 

 rain it is not so pleasant, the roads and paths are 

 then almost impassable owing to mud ; the tall coarse 

 grass when wet is very tiring to walk through, and 

 the mist or vapour covering the marshes all around 

 renders the journey very monotonous, which is 

 occasionally varied by the necessity of jumping a 

 tolerably wide and deep dyke, or clambering over 

 very high fences to avoid making a detour of several 

 miles. Sometimes, too, mishap befalls the unwary 



