1/4 NEW YORK STATE MUSEUM 



17.8 mm. Here there are two sizes about equally abundant: one 

 size varying from 16 mm x 12.4 mm to 17.5 mm x 13.8 mm and 

 the other, from 13.4 mm x 10.8 mm to 15.8 mm x 12.5 mm. None 

 of the very large specimens was found in the vicinity of Chimney 

 Point. One specimen was found measuring 17.2 mm x 14 mm. 

 The large specimens found vary from 14 mm x 10.8 mm to 14.7 mm x 



1 1.6 mm and 14.8 mm x 11. 3 mm; average specimens vary from 



12. 1 mm x 10 mm to 13.5 mm x 10.8 mm and 13.7 mm x 10. 1 mm; 

 but the majority of the shells run smaller, measuring 10 mm x 8.2 mm 

 to 1 1.6 mm x 9.2 mm. 



Yoldia arctica has been found almost as far south as 

 Macoma groenlandica. It has been collected at fewer 

 localities and in smaller numbers than the latter; but it nevertheless 

 shows the same gradual decrease in size southward. Just north of 

 Chimney Point, the most southern locality for the species, the 

 occurrence is very rare, so that few specimens were collected; seven 

 fragmentary shells (four of them half shells) were found and pieces 

 of five other half shells. So far as measurements can be made 

 these shells vary from 8.7 mm x 5.5 mm to 9.5 mm x 6.1 mm and 

 9 mm x 6.4 mm. Comparison of shells from this locality with 

 recent shells and those from the Montreal section can be made only 

 approximately because of the small number to judge from. All the 

 shells found run small, and since those found farther north run 

 as small or smaller, the small size of the Chimney Point shells I think 

 may be accepted without question. I am rather inclined to believe 

 that a larger series of shells from this place would show that those 

 in our possession are an expression of the larger sizes of the shell 

 and that the average individual runs smaller. Typical adult recent 

 forms of Yoldia arctica vary from 19.5 mm x 12 mm to 



20.7 mm x 14 mm; at Montreal typical adult shells were found 

 varying from 17.2 mm x 11.2 mm to 19.3 mm x 11.8 mm and 



19.2 mm x 1 1.9 mm. Approximately, then, the Chimney Point 

 shells are less than one-half the size of the recent shells and about 

 one-half the size of the Montreal specimens. (See plate 2, figures 

 4, 5- 6.) 



Yoldia arctica was collected in largest numbers at 

 Ottawa and Port Kent, N. Y., and is apparently more abundant 

 at the latter place. At Willsboro this species was rare in occurrence, 

 though not so infrequent as at Chimney Point. The largest indi- 

 viduals here vary from 9 mm x 5.6 mm to 9.8 mm x 6.3 mm, while 

 the average specimens measure from 7.1 mm x 4.6 mm to 8.8 mm x 

 5.7 mm. The average specimens vary from a little over one-third 

 to less than one-half the size of the recent specimens and from one- 



