148 



The Molluscan Family Plaiiorbidae 



maqnificum 



pihhryi 



pilsbryi 



pilsbryi 



filsbryi 



itifnicdriiitdum 



injrdciin nittam 



infracarinatum. 



infracarinatum 



infracarinatum 



corpulentum 



corpulentum 



corpulentum 



multicostatum 



rmdticostatum, 



viulticoi^tntum 



rcrmilidiicnse 



vermiUuncnse 



ivhiteavesi 



subcrenatum 



subcrenatum 



var. 

 subcrenatum 



var. 

 subcrenatum 



var. 

 subcrenatum 

 plexatum 

 plexatum 

 plexatum 

 plexatum 

 plexatum 

 horni 

 oregonense 

 occidentale 

 traskii 

 californiense 

 calif orniense 

 californiense 



42-1-42 

 27-1-27 

 27-1-27 

 28-1-28 

 28-1-28 

 32-1-32 

 31-1-31 

 25-1-25 

 30-1-30 

 32-1-32 

 36-1-36 

 25-1-25 

 32-1-32 

 40-1-40 



to 43-1-43 

 to 29-1-29 

 to 29-1-29 

 to 29-1-29 



to 37- 



to 38- 

 to27- 

 to37- 

 to 35- 

 to 41- 

 to 28- 

 to 35- 

 to45- 



1-37 

 1-38 

 1-27 

 1-37 

 1-35 

 1-41 

 1-28 

 1-35 

 1-45 



38-1-38 to 41-1-41 

 30-1-30 to 37-1-37 

 30-1-30 to 31-1-31 

 25-1-25 to 27-1-27 

 36-1-36 to 42-1-42 

 25-1-25 to 27-1-27 

 29-1-29 to 32-1-32 



Wilmington, North Carolina 

 Chetek L., Wisconsin 

 Prairie L., Wisconsin 

 Chetek L., Wisconsin 

 Moose Ear Creek, Wisconsin 

 Basswood R., Ontario 

 Bimaji L., Ontario 

 As above (immature) 

 Mille Lacs, Ontario 

 Rideau R., Ontario 

 Lake La Croix, Ontario 

 As above (immature) 

 Knife Lake, Minnesota 

 Kahnipiminanikok L., 



Minnesota 

 Mille Lacs swamp, Ontario 

 As above (immature) 

 Vermilion L., Minnesota 

 As above (immature) 

 Mille Lacs, Ontario 

 Gypsum, Colorado 

 Pass Lake, Washington 



180 



180-185 



205 



185 



185 



140-163 



140-151 



140-153 



140-155 



171-177 



165-190 



109-117 



140-150 



163-170 



145-150 



152 



120-123 



119 



139-154 



123-130 



150-160 



P. Bartsch 

 F. C. Baker 

 F. C. Baker 

 F. C. Baker 

 F. C. Baker 

 A. R. Cahn 

 A. R. Cahn 

 A. R. Cahn 

 A. R. Cahn 

 A. LaRocque 

 A. R. Cahn 

 A. R. Cahn 

 A. R. Cahn 

 A. R. Cahn 



A. R. Cahn 

 A. R. Cahn 

 F. C. Baker 

 F. C. Baker 

 A. R. Cahn 

 J. Henderson 

 J. Henderson 



28-1-28 to 29-1-29 Lost Lake, Washington 



134-146 J. Henderson 



28-1-28 to 31-1-31 Ponchlla L., Washington 175-180 J.Henderson 



30-1-30 to 32-1-32 McMurrav, Washington 150-170 J.Henderson 



26-1-26 to 30-1-30 Columbine L., Colorado 140-173 J. Henderson 



25-1-25 to 30-1-30 Smartweed L., Colorado 155-170 J.Henderson 



26-1-26 to 30-1-30 Grand Mesa, Colorado 155 J. Henderson 



27-1-27 to 28-1-28 Gocseberrv Creek, Utah 150-165 J. Henderson 



27-1-27 to 31-1-31 Rexburg, Idaho 145-155 J. Henderson 



32-1-32 Paul Lake, British Columl)ia 110-114 D. S. Rawson 



20-1-20 to 21-1-21 Tooele Co., Utah 111-117 J.Henderson 



31-1-31 to 32-1-32 Klamath L., Oregon 150-160 J.Henderson 



28-1-28 to 30-1-30 Kern Lake, California 161-182 S. Siegfus 



24-1-24 to 25-1-25 Shandon, California 155-160 Hanna & Church 



26-1-26 to 27-1-27 San Juan R., California 150 J. D. Hanna 



24-1-24 to 27-1-27 Near Redlands, California 140-157 S. S. Berrv 



T.\BLE Showing Range of Formulae in Different Species 



2S to 27 

 trivolvis 

 pseudotrivolvis 

 chautauquense 

 californiense 



25 to 28 

 fallax 

 lentum 

 subcrenatum 

 plexatum 



20 to 21 

 truncatum 

 oregonense 



28 to 32 

 subcrenatum var. 

 occidentale 

 traskii 



32 to 47 

 infracarinatum 

 corpulentum 

 multicostatum 

 whiteavesi 

 horni 



This table shows that, while there is wide variation in the formulae of 

 the radulae in Pierosoma, the range within the species is fairly constant. 

 The difference in many membranes is due to the presence of several extra 

 marginal teeth on some radulae which do not appear on others. It is to be 

 observed, also, that the immature animal usually has a smaller formula 

 than the same species when adult. This is noted in the table under several 

 species {infracarinatum, corpulentum, vermilionense, and multicostatum). 

 Magnificum has the largest formula, 42-1-42 to 43-1-43. 



Geographical Distribution. The subgenus Pierosoma is distributed 

 from Ungava, Labrador, Mackenzie, and Alaska southward to Georgia, 

 Louisiana, Texas, and California, the whole of Mexico, and southward, on 

 the west coast of South America, to Peru. In the West Indies, it is known 



