INLAND FISHERIES. 81 



in Figure I are, of course, respresentative, and show one or two 

 curious facts which would appear in anj^ similar series. 



The first of these is that the small rounded shell, as already 

 described, becomes relatively much elongated. Again, in the 

 shell A of a millimeter in length, the umbo appears near the 

 middle of the shell, and then rapidly shifts its position anteriorly 

 as the creature becomes older. In outlines 9 and 10 in the series 

 (in individuals 6 and Ih millimeters in length respectively), the 

 umbones are being gradually moved back toward the middle of 

 the shell, and this is continued in older shells until, as in the 

 adidt, they have again assumed a position about equally distant 

 from the anterior and posterior extremities. This shifting in the 

 position of the umbones is of course due to the fact that the shell 

 for a time grows more rapidly posteriorly, and. at a later period 

 the anterior part has a period of more rapid growth. 



In shells not longer than 2 millimeters, it is not difficult to de- 

 tect the usual tooth in the left valve (as well as the excavation in 

 the right), which Gould and Binney describe in the adult as erect, 

 " rounded at its summit, of about equal breadth and height ; its 

 inner face is smooth and rounded ; its outer face is divided into 

 two portions, the largest of which is spoonshaped, the other flat, 

 and traversed across the middle by a grooved ridge, which pro- 

 jects beyond the margin of the tooth like a smaller tooth." This 

 description may be easily applied to the small shell. 



In the smallest forms examined there was a concrescence of the 

 mantle folds similar to the condition in the adult. There can be 

 no doubt, as appears from the enumeration of these peculiar 

 anatomical conditions, but that the small form here described is 

 Mya are?mria. 



ATTACHMENT. 



One of the most interesting features of the life-history of the 



long necked clam — interesting from an economic as well as from a 



scientific point of view, as I shall attempt to show — is the fact that 



it is attached by a byssus to foreign objects during a considerable 



11 



