272 MEMOIRS OF THE CARNEGIE MUSEUM. 



Hinge well-developed. Pseudocardinals one or two in left, one or two in 

 right valve, not very large and not heavy, compressed, subtriangular, somewhat 

 crenulated. Laterals long and thin. No interdentum. Beak-cavity shallow. 

 Dorsal muscle-scars in beak-cavity. Adductor-scars distinct, and moderately 

 impressed anteriorly, less distinct posteriorly. Nacre silvery white, often cream- 

 color or salmon toward the beak-cavity, highly iridescent posteriorly. 



Sexual differences of the shell well marked. In the male the shell tapers 

 uniformly behind into the posterior point, and the lower margin has a rather 

 uniform curve. In the female the lower margin is distinctly produced in the 

 postbasal portion, there forming a broad, rounded projection, behind which the 

 lower margin slopes up more suddenly, and is at this point straight or even slightly 



concave. ^^^ 



L. 

 Size: 1. Yardley, Cat. No. 61.3525 (largest d") 77 mm. 



2. Erie, Cat. No. 61.4088 (c?) 102 " 



3. do. Cat. No. 61.4837 ( 9 ) 93 " 



4. do. Cat. No. 61.4083 (cf ) 89 " 



5. do. Cat. No. 61.4088 ( 9 ) 71 " 



6. do. " " do. (9) 58 " 



Soft parts (See Ortmann, 1912, p. 343). Glochidia (See Lea, Obs. XIII, 1874, 

 PL 21, fig. 2; Ortmann, 1912, PI. 20, fig. 8). 



Breeding season: Conner (1907) mentions this species as breeding all the year 

 round. From the eastern part of the state I have only two records for gravid 

 females: Sept. 15, 1905 and May 10, 1909, in both cases with glochidia. From 

 Lake Erie I have the following records: end of August, 1909 (eggs), and May 21, 

 1909; May 22, 1909; May 24, 1909; June 2, 1908; June 3, 1908; July 7, 1910. 

 The dates in early summer furnished glochidia, and on the two last ones, dis- 

 charging females were found. On and after July 8 numerous females were col- 

 lected, but none were gravid, so that in Lake Erie, as I have shown (1912, p. 343), 

 a distinct interim exists in July and at' the beginning of August. 



Remarks: This is a species quite easily recognized by its lance-head outline, 

 dull olive-green color, with only indistinct rays, and hght-colored nacre. How- 

 ever, it resembles, principally in the male sex certain other species, for instance 

 Elliptio cupreus (Rafinesque) and E. fisherianus (Lea), and indeed, specimens of 

 the latter have been confounded by Conrad with it. E. cupreus and E. fisJierianus 

 generally have a differently colored nacre (coppery or purple), and differ in the 



"' In old males, there is sometimes a short concavity of the lower margin immediately in front of 

 the posterior end. Tliis is due to a downward deflection of the posterior end, such as is often observed in 

 old specimens of other species. 



