202 



HARDWICK&S SCIENCE-GOSSIP. 



A DAY'S SHELL COLLECTING. 

 By Dr. J. W. Williams, m.a. 



ON Wednesday last (June 8th), the weather 

 being fine and the wind freshly blowing, Mrs. 

 Williams and I put into effect a long contemplated 

 day's visit to the River Lea and the necessary ac- 

 companiment of a good search with the scoop into 

 the water for shells. Mr. Wallis Kew had paid 

 fleeting visits with me to the river before, for the 

 same purpose, but we had never stayed so long as to 

 make a thorough examination of the river's bed. On 

 the day of which I am writing this paper we started 

 from my residence, near Regent's Park, a little after 

 ten in the morning, and reached our destination 

 about mid-day, and worked hard and fast till the 

 shades began to lengthen, and the watch to tell us 

 that it was getting near the time of evensong. Never 

 have I spent a more delightful day with nature on the 

 outskirts of London. Never on the outskirts of 

 London have I felt more deeply thrilling in one's 

 very soul the ever-recurring miracle of the mystical 

 yet sanely realistic, Walt Whitman — 



"To me, every hour of the li^ht and dark is a miracle, 

 Every inch of space is a miracle, 

 Every spear of grass — the frames, lirnbs, organs, of men 



and women, and all that concerns them, — 

 All these to me are unspeakably perfect miracles." 



Yet, not like the pure, pure country, but for all 

 that, still enjoyable and delightful. 



I have never taken so many Splnrrium rivkola as I 

 took on that day. Almost every sweep of the scoop 

 brought up some for my collecting box ; and more 

 were taken in one spot than in another, which evi- 

 dently shows a tendency to gregariousness on the 

 part of these, our largest species of the genus 

 Sphrerium. They are pretty bivalves, oval in shape, 

 and much ventricose around, and in the neighbour- 

 hood of the umbones, markedly sculptured with 

 raised stria; running concentric with the umbones 

 which are central in position and bluntly pointed ; 

 the colour is yellowish, banded, or otherwise marked, 

 with blackish brown, and the whole shell carries a 

 length of 19 mill., and a width of 15 mill. The 

 younger ones are much flatter in shape, less ventricose, 

 paler, and not marked with blackish-brown. The 

 shell seems to age first by an extension in length and 

 breadth, and then by an extension in width, for as it 

 becomes older and older, so does it become more 

 ventricose. This ventricosity is more pronounced at 

 the umbo — the umbo being the baby-shell ; so that the 

 adult carries, as well as its own likeness, a miniature 

 of itself. Spharium cortieum were present there too, 

 and specimens of its varieties compressa and flavescens. 

 The former of these varieties was described by Dr. 

 J. E. Gray as " shell rather compressed, margins 

 meeting at an acute angle,"* and by some chance 



* Vide " Shell-Collector's Handbook for the Field," p. 47. 



or other has been overlooked by Dr. Gwyn Jefferys, 

 Rimmer, and Adams ; the latter is paler, not so 

 large, and more globular than the type, and was first 

 described by Macgillivary as Cyclas flavescens on p. 

 246 of his " Molluscs of Aberdeen." Sphcermm 

 corneum is common almost everywhere, but Spharium 

 rivkola is more or less local in its distribution. 



Closely allied to the Sphaeria are the Pisidia, both 

 genera belonging to the family Sphaeriidae, and of the 

 genus Pisidium only one species was taken, viz., 

 Pisidium amnicum. It is an extremely difficult 

 matter to tell the Pisidia from the Sphasria, and 

 although some conchologists will stake their word 

 on the examination of the shell merely, I will not, 

 and must have the animal before I will come to 

 a definite and conclusive diagnosis. It is then, if 

 you have the animal, an easy matter, for if a specimen 

 belongs to the genus Pisidium it has one siphon, and 

 if it belongs to the Sphaeria two siphons ; if it be a 

 very young Anodon or Unio it has no siphons at all. 

 That is the only conclusive test, and that I recom- 

 mend to all shell-workers as the only positive way 

 whereby they can diagnose the genus. Get your one 

 siphon and then tell the species by the shape of the 

 shell if you like ; it is triangular in Pisidium amnicum 

 and P. fontinale, oval in P. pusillnm, round in P. 

 nitidum, and oblong in P. roscum. Pisidium amnicum 

 and P. fontinale are the only two alike in the shape of 

 the shell, it being triangular in both species, but the 

 shell of P. fontinale is far more tumid (almost cuboid), 

 more transparent, thinner, and not so deeply grooved 

 concentrically. I cannot pass by the Pisidia without 

 mentioning that Pisidium pusillum differs from all 

 other lamellibranchs in having the sexes united 

 in the same individual ; just as Limax (Eulimax) 

 Icevis differs from all the Pulmonata in having the 

 sexes distinct. 



Of the Anodons I took one Anodonta anatina, and 

 of the Unios, three Unio tumidus. I have not much 

 to say of these except that U. tumidus is the most 

 plentiful of the Unionidae in the River Lea, and that 

 A. anatina can be easily distinguished from A. cygnca 

 by the angle which its ligament makes with the lower 

 margin of its shell, and that U. tumidus can be as 

 readily distinguished from U. pictorum by the wrinkled 

 condition on its umbones. Dr. Henry Woodward 

 has lately considered it his duty to make the statement 

 that A. anatina is but a variety of A. cygnea, and in 

 the absence of his giving any proofs for this somewhat 

 uncanonical assertion, and on the grounds of the 

 difference well marked between the two types, I must 

 hold his idea as arguing badly for his knowledge of 

 the constitution of a species and of a variety. 

 Anatomical differences apart, there is enough in the 

 shell to warrant us in still holding on to it as a good 

 species. 



Passing on now to what Cuvier termed the 

 Malacozoa Gastropoda ; of the family Paludinidae I 

 took, Paludina vivipara and Bythinia tentaculata. 



