ORTMANN: monograph of the naiades of PENNSYLVANIA. 101 



well as from the Erie Canal and the Moliawk River (Call) and it belongs to the 



few species, which have gone along this route probably in very recent times. 



Whether this stock came from Lake Erie or from the upper Allegheny, remains 



to be seen. 



Elliptio dilatatus sterkii Grier (1918). 



Unio gibbosus Barnes (Sterki, 1907a, p. 392) small form; Unio gibbosus Barnes 

 (Ortmann, 19096, p. 203) lake form; Unio gibbosus Barnes (Walker, 1913, 

 p. 22, map, fig. 2 on p. 30) ; Elliptio dilatatus sterkii Grier, 1918, p. 9. 



Plate VIII, fig. 3. 

 Records from Pennsylvania: 



Ortmann, 1909fc, p. 203 (as form of Unio gtbbo-ius from Lake Erie). 

 Grier, 1918, p. 9. 



Characters of variety: Distinguished from typical E. dilatatus by small size, 

 rather swollen shell, (with the diameter over thirty percent, while it is less in the 

 typical form), the more anterior position of the beaks, and lighter color of the 

 epidermis, which is from yellowish olive to brown (sometimes dark brown), with 

 more distinct rays (chiefly when young). Generally in old shells the posterior 

 slope or the posterior end of the shell is lighter in color (yellowish to rusty brown) • 

 The growth-rests are rather regular, and rather well-marked by concentric dark 

 bands. Nacre mostly lighter, white to light purple, but sometimes as dark as 

 in the typical form. 



L. H. D. Pr.ct. 



Size; 1. Erie, Cat. No. 61.3228 (largest) 87 mm. 4.5 mm. .33 mm. .38 



2. Erie, Cat. No. 61.4628 (c?) typeset 86 " 40 " 33 " .38 



3. do. do. (9) do 77 " 37 " 27 " .35 



4. do. do. (9) do 72 " .33 ' 23 " .32 



5. do. do. (cf) do 58 " 29 " 18 " .31 



Soft parts: They agree entirely with those of typical dilatatus. Glochidia 

 not known. 



Breeding season: Gravid females (with eggs) have been observed on July 8 

 and 12, 1910. 



Remarks: With a rather large number of specimens (over fifty) before me, I 

 am convinced that this is, as Grier has pointed out, a good local race of E. dilatatus. 

 Although the normal form locally does not grow very large, the lake-form is always 

 more swollen (see measurements), and this gives to the shell a rather subcylindrical 

 shape, chiefly so in its anterior part. In the color of the epidermis, young speci- 

 mens of sterkii are distinctly lighter than normal dilatatus, and in consequence of 



