January, 1922.) 



The Canadian Field-Naturalist 



(Trans. 1, p. 40) contains only four species, two 

 of which were not positively identified. Another 

 species was added in the Report of the Concho- 

 logical Branch, read March 13, 1890, and prepared 

 by the writer and the late Rev. Geo. W. Taylor, 

 which gives a catalogue of all the molluscs then 

 known to be found in the vicinity of Ottawa. 

 The success attending Roper and Winkley in 

 Massachusetts and Maine and the encouragement 

 extended by Dr. Sterki induced me to devote 

 special attention to this genus. The result was 

 that in my Preliminary List of Sphaeriidae 

 published in The Naturalist in 1913, I enumerated 

 twenty-three species of Pisidia, several of which 

 were considered new. Since then I have added 

 several others and the field is by no means ex- 

 hausted. So numerous are the localities in which 

 the shells occur that many other species and varie- 

 ties must remain undiscovered. 



33. PisiDiUM VIRGINICUM Gmelin. — Heron 

 found this shell on the beaches of Kettle Island 

 exposed at low water. My only specimens were 



obtained in a similar situation 

 lower down the Ottawa, and by 

 dredging in the pond, prolific in 

 small molluscs, on Duck Island — 

 near the south end. With the 

 p. virginicum, X 2 exception of P. idahoense., which 

 has not been found in Ontario or Quebec, it is the 

 largest known species, attaining frequently a 

 length of 8 mm. It appears to be quite active 

 and makes long and distinct furrows in moving. 

 When mature it is always of a dark brown color 

 near the umbones. 



Mr. A. D. Robertson found P. virginicum 

 abundant in sandy channels in the Georgian Bay 

 (Contributions to Canadian Biology, Fasc. ii, 

 107), but appears not to have noticed there any 

 other shell of the genus. The species has a wide 

 range in the United States east of the Rocky 

 Mountains, and extends even into Alaska and 

 Yukon. 



34. PiSIDIUM IDAHOENSE RoPER. This shell 

 ranges from Idaho westward to Washington and 

 northward through British Columbia into Yukon. 

 East of the Rockies it is found in the United 

 States only in Michigan. Farther east it is not 

 known to occur except in Prince Edward Island 

 where it was found by Mr. C. Ives. This gentle- 

 man began the study of the mollusca after attain- 

 ing the age of three score years and ten, and then 

 became an indefatigable collector, especially of 

 the smaller marine forms like odostomia, discover- 

 ing several previously unknown. It is a matter of 

 profound regret to many that impaired vision has 

 prevented a continuance of his fruitful labors. 

 Other pisidia found by him near his home are 



compressum, abditum and variabile. His sendings 

 of P. idahoense from a pond near the east end of 

 Prince Edward Island are identical in every 

 characteristic with co-types received many years 

 ago from Mr. Roper. The shell is of great size 

 in comparison with the largest other species of the 

 genus. I have several specimens from Mr. Ives 

 which exceed 18 mm. in length. 



35. PiSIDIUM VARIABILE Prime. This species 

 occurs in great numbers in many places near 

 Ottawa. One such locality where no other 

 member of the genus is found is a ditch running 

 east and west on the Shouldis farm on Carling 

 Avenue, south of the wood lot. When mature it 

 is but slightly smaller than virginicum and never 

 as dark in color. The shell is solid, inflated, 

 inequilateral and oblique. The umbones are 

 greatly elevated, full and prominent. In the 

 vicinity of Toronto it is quite a common shell and 

 is among the species collected by Mclnnes in the 

 Attawapiscat. 



36. PiSIDIUM COMPRESSUM Prime. No shell of 

 the genus is more common than this in the vicinity 

 of Ottawa. It abounds in Hemlock Lake especial- 

 ly near the south-west angle where the banks of 

 marl reach to the water's edge, and living molluscs 

 form their shells from the remains of ancestors 

 long dead. In Nepean it is found in Cave Creek 

 and on the Magee and Shouldis farms; in the 

 Ottawa on the shoals above Britannia pier; at 

 Cornwall in the canal; in Lake Erie at Port 

 Ryerse; and near Toronto at Richmond Hill and 

 in the Etobicoke. On the Quebec side of the 

 Ottawa it occurs in Chilcott Lake, near the outlet 

 from the orchid swamp. 



37. PiSIDIUM COMPRESSUM PELLUCIDL^I Sterki. 



At one time Dr. Sterki regarded this shell as 

 entitled to specific rank. In his PreHminary 

 Catalogue, however, he treats it ?.s a variety of 

 compressum from which it differs in size, being 

 smaller. It is also less high, the beaks are less 

 pointed; surface with lighter stripe, shell trans- 

 lucent. 



38. PiSIDIUM SPLENDIDULUM Sterki. A few 

 small shells from Magee's Creek south of the 

 Richmond Road (my No. 2547) are thought to 

 belong to this widely distributed and variable 

 species. It is desirable that additional specimens 

 should be obtained. None could be found in the 

 summer of 1921 on the only occasion on which I 

 collected in this stream. 



39. PiSIDIUM GLABELLUM Sterki. Shells from 

 the stream south and west of Graham Bay Station 

 which I sent to Dr. Sterki in 1911 (his No. 6812) 

 are referred to in his description of P. glabellum 

 (Nautilus, XXVI, 137). He considered them 

 attributable to the new species though somewhat 



