SCIENCE-GOSSIP. 



39 



PLEISTOCENE MOLLUSCA OF CRAYFORD. 



By A. Santer Kennard. 



HpHERE are few, if any, pleistocene sections in 

 England which are better known than the 

 classic one at Stoneham's Pit, Crayford. It was 

 first described by Professor J. Morris in 1838, and 

 a list of thirteen species of mollusca given, including 

 Unio littoralis, then first described as a British 

 fossil. Since then it has been many times described 

 and its fossils enumerated more or less accurately. 

 In 1890, Mr. B. B. Woodward, after a careful 

 examination of all existing material and 

 records, extended the number of fossil 

 mollusca to forty-six species, forty-two 

 from existing specimens, three on the 

 authority of Mr. A. Tylor, and one on 

 that of Professor J. Morris. (Proc. Geol. 

 Ass., August, 1890.) 



During the past year I have been able 

 to devote a little time to this deposit, 

 and I am now able to add two new 

 species, Littorina rudis and Limax agrestis, 

 both represented by single examples, 

 which I have presented to the Natural 

 History Museum, South Kensington. 

 Limax agrestis has already been recorded from the 

 contemporary beds at Grays, Essex. The presence 

 of Littorina rudis is, however, more noteworthy. 

 It is a very dwarfed example, but after careful 

 comparison with some brackish water-forms from 

 Tilbury, Essex, I referred it to that species. I 

 endeavoured to get the 

 identification confirmed, 

 but no one would venture 

 an opinion until lately, when 

 Mr. E. R. Sykes, F.Z.S., 

 concurred in referring it to 

 Littorina rudis. The pre- 

 sence of this species together 

 with Paludestvina ventrosa, 

 already known from these 

 beds, undoubtedly points to 

 the proximity of estuarine 

 conditions. Both examples 

 were obtained from the bed 

 numbered 5, page 438, vol. 

 i., "Geology of London." 



In Science-Gossip (1890, page 4), Mr. T 

 Cockerell figured an example of Pisidium amnicum 

 from Crayford, showing constriction of the valve, 

 which he says is common in the Crayford Pisidia 

 and Sphasria. Further on he refers to " the con- 

 striction of the valve which is so frequently seen in 

 the fossil examples of Pisidium and Sph^rium from 

 Crayford. Why a character, apparently monstral, 

 should occur so commonly among these shells is 



LlMNEA PALUSTRIS. 

 Sph^erium CORNEUM 



Unio littoralis, from Crayford. 



D. A. 



more than I can tell." This mended fracture is 

 found in both valves, and varies somewhat in size 

 and shape. In one example in my collection it 

 resembles the letter "|", the top fracture being in the 

 middle of the valve. In another example, two 

 fracture lines start from the centre of the shell at 

 right angles to each other, but do not reach the 

 margin. In those examples where the fracture 

 extends to the margin, the angle varies, sometimes 

 being forty-five degrees, more often 

 seventy-five and occasionally ninety de- 

 grees. So far as I know, this feature 

 has not been found elsewhere. As to 

 the cause, Mr. Cockerell has suggested 

 a parasite, while Mr. B. B. Woodward 

 is of opinion that it was caused by 

 mechanical means such as pressure from 

 without, and with this latter opinion I 

 agree. 



I must, however, strongly object to 

 the terms "common" and "frequent' 

 as the following figures will show. Out 

 of 572 valves of Pisidium fontinale, 2 

 are fractured ; of 3,722 of Pamnicum 18 are 

 fractured ; while of 82 of P. pusillum and 422 of 

 Sphazrium corneum all are of the normal form. That 

 is a total of 20 out of 4,798 ; a proportion 

 which can scarcely be characterized as common. 

 I may add that I possess a valve of Unio littoralis 

 which possesses this frac- 

 ture, a fact which is cer- 

 tainly at variance with the 

 parasite theory. Of the 

 forty-six species enumer- 

 ated by Mr. Woodward I 

 have found no less than 

 thirty-seven. Of the re- 

 mainder there are. four 

 species — Hyalinia radiatula, 

 H. crystallina, H. nitida, 

 and Carychium minimum — 

 of which there are no 

 known examples. Cochlicopa 

 lubrica, Clausilia rugosa, 

 and Helix arbustorum are 

 represented by unique examples in the Natural 

 History Museum, while Paludestrina ventrosa and 

 Paludina contecta are nearly as rare. Helix pulehella 

 is the commonest Helix, while H. hispida is the 

 rarest. The examples of H. eaperata are much 

 smaller than living examples, and retain traces of 

 colouring. Helix nemoralis is usually represented 

 by fragments, though there are two fine perfect 

 examples at South Kensington, Pupa museontm is 



