Image via Wikipedia G. W. C. B., Baltimore, Maryland, writes: "In some sections of country pumpkins, or at least such as are recognized as such in other sections are called squashes and then again in other sections this order of recognition is exactly reversed. Will you please define the difference between pumpkins and squashes, so we novices can make the distinction also."
We submitted your inquiry to Prof. L. H. Bailey of Cornell University, who kindly replies as follows:
It is impossible to give any distinctions between pumpkins and squashes because the vernacular names are used very indiscriminately. Ordinarily, what people in Europe call pumpkins are what we call squashes. Perhaps I can best answer by saying that there are three types of pumpkin-like plants which we grow. One type is characterized by a soft, round stem to the fruit, and to this type belong the true squashes, like the Hubbard, Boston Marrow, Turban, Mammoth Chili, and the like. This species is Cucurbita maxima. Another type is characterized by a very hard and deep-five-cornered stem, and this includes the true field pumpkins which are used so much for stock and for pies. To this type also belong the summer bush squashes like the Crookneck, and scallop varieties. This type is Cucurbita Pepo. This third type is characterized by a rather firm, cylindrical stem which has a large expansion where it joins the fruit and it includes the Cushaw, Canada Crookneck and Japan Crookneck types. This type is Cucurbita moschata. -L. H. Bailey (From "Gardening, Vol. IV, 1896)