S3 



ON THE RANGE OF PISIDIUM SUPINUM Schmidt. 



By CHAS. OLDHAM. 



(Read before llie Societj-, November loth, 1909). 



During the past summer I have taken Pisidiiim supinuin at several 

 places in the Grand Junction Canal; in Middlesex, at Harefield; in 

 Hertfordshire, at Rickmansworth, Tring and Wilstone; in Bucking- 

 hamshire, at Marsworth and Slapton; and in Northamptonshire, at 

 Blisworth. In every case this species was associated with P. anmiawi 

 and P. henslotvanwn, and usually with P. subtruncatuin. The bed 

 of the canal is, in most places, stony, but here and there some silt 

 and mud provide congenial quarters for bivalve moUusca. Perhaps 

 the favourite habitat of snpimun was in the silt that had collected 

 about the roots of Potaniogelon pectinatns, a plant that grows sparingly 

 in patches in the stony bed, but at Slapton I took several specimens 

 in thick black mud in which Unio tumidus and U. pictoriim were 

 living. In all the localities I have mentioned the dominant form is 

 the type, in which the umbones are furnished with appendicula 

 similar to those in P. henslowanmn^ but at Harefield, Wilstone and 

 Marsworth I took a variety in which the appendicula are lacking. 

 At Marsworth, associated with the other two, a third form occurs. 

 This is oval, not unlike typical P. p2(si/Iu!/i in outline, very glossy, 

 strongly striated, and lacks the appendicula. It may be worth*men- 

 tioning that in embryonic shells of the typical form that I extracted 

 from specimens taken at Rickmansworth in July, the appendicula 

 were situate in the middle of the valves, as they are in P. henslowatiiun 

 of that age, and not at the umbones as they are in mature shells. 



Mr. B. B. Woodward, in looking over my collection recently, kindly 

 called my attention to specimens of P. supinuin which I had over- 

 looked. I collected them in the Union Canal at Aylestone, near 

 Leicester, in July, 1892, and in a pond at Kelsall, Cheshire, in June, 

 1894. The shells, in both cases, are of the non-appendiculate variety. 



Localities for Hygromia revelata (Michaud). —This species has been 

 recorded from " Plymouth,"' but this rather vague indicalion covers Such an exten- 

 sive area that I feel justified in recording that I recently found the shell in a typical 

 habitat on the cliffs above ^Whitsand Bay, beyond Rame Head. This is, of 

 course, on the Cornish side of Plymouth Sound. I have also collected H. revelaia 

 at the Lizard, Land's End, and Kynance Cove. — J. R. lk B. Tomlin {Read hefo7-e 

 the Society, November loth, 1909). 



I The usual local spelling. 



