N 



ovember, 



1919] 



The Canadian Field-Naturalist 



85 



delightful impressions that may be derived from 

 flowers and birds, and the many strange four and 

 six-footed creatures that he will encounter on his 

 rambles in places seldom frequented by man. 



A very fine form of 5. sulcatum occurs on the 

 Scott Graham farm in Nepean, now called Bri- 

 tannia Highlands. In dry seasons the narrow bot- 

 tom of the stream lying about halfway between 

 Carling Avenue and the Grand Trunk railway is 

 exposed for some distance west of the boundary of 

 the Shouldis farm. The shell may then be easily 

 found in considerable numbers. At other times 

 collecting is slew and difficult, even though the 

 collector is equipped with a good dredge, and 

 what are indispensable in such localities rubber 

 boots. This stream is again productive near its 

 outlet into the Ottawa below the Deschenes rapids. 



conditions of environment. In fact nothing is so 

 wonderful in nature as the adherence to type of 

 every organized being properly regarded as a 

 species. More interest is, however, manifested in 

 departures from the normal than in persistence of 

 type, just as variant races of men, like the giant 

 Patagonians and pygmy Papuans, commonly at- 

 tract more attention than races of ordinary stature. 

 Variations from the usual form of 5. sulcatum are 

 few and limited. One is found in Bond lake, near 

 Toronto. Another, which is well marked and con- 

 stant, occurs in Masham, north of Ottawa, and, 

 notably, in Lake Gorman, near Brudenell, in the 

 county of Renfrew, at an elevation of about eleven 

 hundred feet above sea level. 



Dr. Sterki thinks it entitled to rank as a variety 

 and calls it palmaiuiu.' He describes it as smaller 



OS. 



aa^^ 



a rp - 



ot'- 



Vh 



a. a. Anterior adductor mu.scle. 

 a. p. Ant. retractor-pedis muscle. 

 ar.^Auriele. 



b. Byssal gland rudiment. 

 bs. Branchial sii)hon. 

 eg. Cerebral ganglion. 

 cs. Cloacal siphon. 



f. Foot, 

 ig. Inner gill. 



1. Liver. 



Fair specimens are obtainable in shallow water 

 at Graham Bay station, at the intersection of the 

 Richmond road and the Grand Trunk railway. A 

 few m.iles farther to the southwest the shell is com- 

 mon in the creek north of Stittville ; but nowhere 

 have I found it in such numbers as in the stream 

 about a hundred yards west of Ste. Justine station, 

 in the county of Vaudreuil. In either place the 

 shell may be readily collected in large numbers by 

 means of a dredge with a quarter-inch mesh, such 

 as is afforded by a kitchen utensil in common use. 



As S. sulcatum is a true species, with an objective 

 existence not depending on the opinion or whim of 

 any systematist, it does not vary greatly in its 

 characteristic features throughout the vast area 

 over which it is desseminated, though it is 

 occasionally modified in appearance by different 



m Mantle. 



ob. Organ of Bojanns. 



06. Oesophagus. 



ot. Otocyst. 



pa. Posterior adductor muscle. 



pg. Pedal ganglion. 

 prp. Post retractor-pedis muscle, 

 psg. Parie to-splanchnic ganglion. 



ro. Reproductive organs, 

 t. Male follicle. 



than the common or typical sulcatum, more in- 

 equipartite, the beaks being markedly anterior; less 

 inflated, especially flattened over the lower part of 

 the valves, more truncate anteriorly and posteriorly, 

 inferior margin less curved; beaks narrower and 

 little elevated; surface striae slighter; shell and 

 hinge slighter. 



In Lake Gorman the shell is quite abundant 

 buried about an inch in the sand of the bay near 

 the boathouse on the Rockingham road. 



The animal of the variety palmatum has not been 

 described. It is probably not distinguishable from 

 the normal form represented in the following illus- 

 tration, which may be regarded as typical of the 

 anatomy of all the genus: 



4Preliminarv Catalogue of N. A. Sphaerlldea, 

 An. Carg. Mus., Vol. X (1916), p. 432. 



