128 The MoUuscan Family Planorbidae 



Helisoma anccps royalense (Walker). 



Bamiji Lake, Ontario 25-1-25 to 27-1-27 1-S 9 Plate 54, fig. 2 



There are 170 rows of teeth. 

 Helisoma anceps cahni F. C. Baker. 

 Big Muskallonge Lake, Ontario 27-1-27 to 27-1-27 1-6 7-9 Plate 54, fig. 3 



There are 160 rows of teeth. 

 Helisoma anceps latchfordi (Pilsbry). 

 Meach Lake, Quebec 27-1-27 to 30-1-30 1-6 7-9 Plate 54, fig. 4 



There are 190 rows of teeth. 



For the above data more than forty siiecimens have been examined. In 

 general form of teetli, there is complete agreement in all radulac examined, 

 both from the same locality and from different places. The formulae vary 

 and along with this variation, the numbers of lateral and intermediate 

 teeth likewise vary. 



Abnormal teeth arc connnon in radulae of Heluoma anceps. In a speci- 

 men from Maple River, Michigan, the fourth lateral of the fifteenth row 

 had the ectocone broken up into four small cusps (plate 53, fig. 1). In a 

 specimen from Chautauqua Lake, New York, the center tooth of the 118th 

 row was broken up into three small cusps and one large cusp. In the first 

 lateral of the same row, the entocone was split into two small cusps 

 (plate 53, fig. 2). In a specimen from Unionville, Connecticut, the fifth 

 lateral of the ninetieth row had a split ectocone. The 8th and 9th teeth of 

 this row had the intermediate in unusual form. This row shows the shape 

 of the teeth on the left side of the membrane (plate 53, fig. 3, lower row). 



In the races of anceps, the same tendency to form abnormal teeth is 

 observed. A specimen of saiji from Bayfield, Wisconsin, had the center 

 tooth of the seventy-fifth row with three small cusps on the left side and 

 one small cusp on the right side of a central cusp. All of the laterals in 

 this row had the entocone broken up into two small cusps (plate 53, fig. 4, 

 lower right row). In a radula of percarinahmi from Douglas Lake, Michi- 

 gan, the first and second laterals of the 100th row had the entocone split 

 into two smaller cusps (plate 54, fig. 1, lower row). A specimen of latch- 

 fordi, in the sixtieth row, had the central tooth with an extra cusp on each 

 side of two smaller central cusps (plate 54, fig. 4, 60). All of the teeth of 

 this race examined had two very small denticulations on the edge of the 

 reflection above the ectocones (plate 54, fig. 4). 



Geographical Distribution. The species of typical Helisoma inhabit 

 North America from British America (Hudsons Bay) southward to Lou- 

 isiana and Alabama and westward to the Rocky INIountains. 



Species Considered as Valid. This, the typical subgenus of the genus 

 Helisoma, contains one sj^ecies with many races and a second species with 

 two recognizable races. 



Helisoma anceps anceps (Menke) 1830 Helisoma anceps unicarinatum (Halde- 

 (=^ Planorhis bicarinatus Say 1819 man) 



(preoccupied), P. antrosus Conrad, Helisoma anccps striatum (F. C. Baker) 



1834) Helisoma anceps cahni F. C. Baker 



Helisoma anceps sayi F. C. Baker Helisoma anceps latchfordi (Pilsbry) 



Helisoma anceps shellense F. C. Baker Helisoma anceps portagensis (F. C. 

 Helisoma anceps percarinatum (Walker) Baker) 



Helisom.a anceps royalense (Walker) Helisoma anceps aroostookense (Pilsbry) 



Helisoma anceps ruski F. C. Baker Helisoma eucosmium (Bartsch) 



Helisoma anceps jordanense (Winslow) Helisoma eucosmium vaughani (Bartsch) 



