WOODWARD : ON SOME SPECIES OF PISIDIUM. 211 



Dr. Westerlund. The former set, labelled by Westerlund himself, 

 proved to consist of two opened and one closed pair of P. pusillum, 

 and two opened pairs of P. hibernicum. The second set included two 

 valves of P. cinereum, f. lacustris, and four valves of immature 

 P. pusillum. 



Dr. Nils Hj. Odhner most obligingly sent for my inspection from 

 the Stockholm Museum a tube labelled in Clessin's handwriting 

 "Pis.parvulumCless I Bleckinge | Igt AVesterlund | com. Clessin". 

 This gathering included two whole P. milium, one whole P. nitidum, 

 and five valves of P. hibernicum. Dr. Odhner informed me that 

 he had received from Berlin one of the original specimens of the 

 variety which proved to be P. ohtusale. 



Dr. D. Greyer of Stuttgart has been so good as to examine Clessin's 

 collection there. He reports finding three gatherings of P. parvulum, 

 which on inspection resolved into : small ohtusale, half-grown 

 nitidum, young cinereum, and three specimens of milium ! 



It is therefore quite obvious that Pisidium jparvulum of Clessin 

 and Westerlund is a composite of species all otherwise named and 

 that the name must disappear from, literature. The form, there- 

 fore, which of late has passed with us under that name, will take 

 Stelfox's happily suggested designation, and be known as : — 



Pisidium torquatum, Stelfox. 



When this species was first added to the British fauna in 1916 

 by Mr. E. A. Phillips,^^ the only standard of comparison which we 

 possessed were the squarrose examples Dr. Johansen had sent me 

 from Fursoe, and I was unable to assent to the reference of the whole 

 of the specimens claimed as " parvulum " to that species and main- 

 tained that some, and especially the very triangular forms from the 

 Thames Valley deposits, were merely the fry of P. supinum.^^ 



Lately fresh fossil material has come into my hands and I have 

 had the privilege of studying Mr. C. Oldham's collection of this 

 form, and have verified the fact that examples quite as triangular 

 as those in the Thames Valley deposits occur living at Welshpool. 

 Whilst as to the distinction between torquatum and juvenile supinum, 

 both Dr. Johansen in 191 4 ^^ and Mr. Stelfox in his useful paper on 

 " The Pisidium Fauna of the Grand Junction Canal ",^* point out 

 that there is a difference in the appendiculse in the two forms. 

 Strictly speaking they are not so much appendicular present in 

 torquatum as a discontinuous junction between the nepionic and 

 adolescent shell, somewhat similar to that in Sphcerium lacustre, 

 resulting in crescentic ridges conformable to the " lines of growth " ; 

 whereas in supinum and henslowanum the shelly ridges, which are 

 sometimes quite sharp, usually cut obliquely across the " lines 



^2 Irish Naturalist, xxv, p. 101. 



" Ann. & Mag. Nat. Hist., ser. vin, vol. xviii, 1916, p. 346. 



" Joum. of Conch., xv, 1918, p. 299. 



