3. The larger species, as the "washboard," "bluepoint," and "mucket," are generally so evidently valueless in the small sizes that shellers do not take them. At least it is not yet of observation that particular injury is being done to these species in this way. 4. To insure the least trouble of enforcement of the law, it is necessary that a minimum size be set, below which no shells of any species may be retained. There are many different species of commercial mussels, and some of them so intergrade as to make exact determination a nice matter in some cases. Distinct size limits for the different species would introduce peculiar difficulties into the practical workings of enforcement; it would be more troublesome to the sheller to observe the law voluntarily, and loopholes for evasion would more easily be found by the offender of wrong intent. Should conditions in certain States or streams subsequently require a higher limit for particular kinds of shells, a supplemental limit may be fixed for designated species; but this could be done without affecting the application of a 2-inch limit as an absolute or universal limit below which no shells of any species could be lawfully taken. It is desirable that few different limits should ever be used, and it seems expedient to have but one size limit until the first legislation shall have been tried out. DETAILS ESSENTIAL TO EFFECTIVE LEGISLATION. In concluding this section emphasis may be laid on the value of certain details of legislation. _Allowable margin of undersized shells._--While it may seem desirable that no undersized shell at any time should be taken away, nevertheless it is necessary to make allowance for a margin of unintentional error. Only if the shellers and buyers were to apply an instrument of measure to each individual shell would all possibility of error be eliminated. The sheller will naturally, after a few measurements, come to judge by the eye, and it is desirable that the law should be somewhat liberal, rather than too stringent in the allowance for mistakes. There should, accordingly, be a supplemental provision that if not more than 5 per cent of the shells by number (not by weight) of any bushel are found to be below the size limit, the law shall not be presumed to be violated. _Illegal possession._--To be practicable of enforcement, the law should be so worded as to make it illegal not only to bring ashore or to offer for sale, but also to have in possession, fresh-water mussels or clams of a size less than 2 inches in greatest dimension. This one provision will obviate much unnecessary expense, as well as undesirable complications in the detection of violations and the prosecution of offenders. Furthermore, since buyers of the shells would be equally liable to prosecution, the effect would be to destroy the market for undersized shells, and thus in the most effective way to restrain the shellers from taking them.