298 JOURNAL OF CONCHOLOGY, VOL. I5, NO. ID, SEPTEMBER, 1918. 



ones. From P. parviihim it differs in its siphon, in its larger c. j, 

 which resembles slightly that of P. casertanuvi^ and in the fact that 

 /. /// does not curve inwards towards the umbo to meet/. /, but on 

 the contrary runs on parallel to it and dies away under the ligament pit. 

 Since the discovery of this species at Cheddington, Mr. Oldham 

 has taken examples at Marsworth in the same county, and in 191 7 

 found it in the canal at Stoke Bruerne, Northamptonshire, and in the 

 Northampton branch of the canal at Rothersthorpe. A specimen 

 from the latter locality is the largest I have seen and has all the 

 appearance of being greatly overgrown. It measures 2'o x I'y x i'2 

 mm., and is not so thickened as the type. Its cardinals are remark- 

 ably developed, c. j being distinctly bifurcate, and its c. 2 resembles 

 that of some P. amnicum {cf. plate 8, figs. 4 and 5). It is most im- 

 probable that this little species is confined to the canal and it is almost 

 certain to turn up in the Thames, Great Ouse, and other rivers. It 

 should also be found in the Pleistocene deposits of ihe London Basin 

 in which all its associates occur commonly. In Ireland we have 

 looked for it in vain in the sands from the rivers that have yielded 

 P. parvidum in some numbers. Collectors if searching for this or 

 the next species should be careful to use a scoop with a very fine 

 mesh, or these two shells will pass through it and escape notice. 

 Mr. Oldham uses a scoop with wire gauze of 324 meshes to the 

 square inch. 



P. parvulum Clessin (?). Plate 8, figs. 2 and 14-21. 



This species appears to be abundant in the canal, and was taken 

 by Mr. Oldham in all the places selected by him for special attention, 

 as well as at places beyond the area dealt with in this paper between 

 Cheddington and Leighton Buzzard ; and at Stoke Bruerne and 

 Rothersthorpe in Northants. In England I have also seen it from 

 the Pleistocene of Grays, Essex, and Crayford, Kent. In the living 

 state it has been taken by Mr. J. E. Cooper in the Thames in several 

 stations from Twickenham in Middlesex to Long Ditton in Surrey ; 

 and by Mr. Oldham in the Kennet and Avon Canal near Seend in 

 Wilts. In Ireland it occurs commonly as a fossil in sand dredged 

 from the rivers Barrow, Nore, Suir and Shannon, and no doubt still 

 lives in all these rivers, as Mr. Phillips has recently taken it alive in 

 the Suck, a tributary of the Shannon, near Ballinasloe, in South 

 Galway. 



Mr. Woodward regards the shells from the Pleistocene and many 

 of our other specimens as the young of P. supinum (see i\nn. Mag. 

 Nat. Hist., series 8, vol. xviii., pp. 346-348, 1916), but I hope that 

 the figures that I give of the latter will enable any conchologist to 

 separate the two species. The coarse striation, larger unibones, and 



