THE NAUTILUS. 53 



stand and let some one else take up the problem and bring it 

 to a conclusion. 



In some places along the Atlantic coast of New Jersey are 

 exposed at low tide stumps of trees and also such turf as is 

 now forming in the meadows behind the line of sand dunes. 

 By this we can infer that the coast line is sinking. This 

 being the case, the dunes are progressing inland, covering up 

 the meadow turf and exposing it again in the ocean beach. 

 Between the dunes and the mainland is oftentimes a bay or 

 a channel. This bay or channel has a muddy bottom as a 

 rule and there the Pecten lives. As the dune line pro- 

 gresses forward the meadow encroaches on the bay, burying 

 the dead shells of the Pecten which are later exposed by the 

 action of the surf and cast on the beach after the dune line 

 has passed over them. 



It would be interesting to test if such a theory were correct 

 and note the direction of the evolution of the Pecten or other 

 form during the time that they were buried. 



An examination of well borings made in the beach might 

 help throw light upon this point. 



Experiments also might be made as to the rate of infiltra- 

 tion of the clay particles into the shell which may be rapid. 

 The author made sections of the shells. These sections show 

 that the clay has penetrated the shell to the center, the pearly 

 layer alone excepted. 



With the geologic evidence from well borings, with the 

 experimental evidence from the rate of infiltration of the clay 

 particles and the comparison of the variation of the blue 

 forms with those now living, a conclusion might be drawn as 

 to the direction of evolution in Pecten. 



In the table which follows, N = the number of shells the 

 rays of which were counted, A==the mean, a- the stand- 

 ard deviation from the mean, C = the coefficient of varia- 

 tion, and P. E. the probable errors of the mean, the stand- 

 ard deviation, and the coefficient of variation. These have 

 been computed by the ordinary methods. With them in 

 lower case are placed similar counts made by Davenport 

 (1900) on Pecten irradmns from several other localities. 



