To help you out with Large vs Small mouth bass, some more details. Below a picture to get it more clear.
Large mouth bass and Small mouth bass are both classed by the scientists as members of the Sunfish family. This group also includes the Crappie, Rock bass and Bluegill —all of which are commonly known to anglers as Panfish.
Large mouth bass are probably the most widely distributed and fished-for game fish in the world. While this great fresh water fighter was originally found only in America from Canada south to the Gulf of Mexico and from the Atlantic to the Rocky Mountains, it has been planted successfully in the Pacific Coast states, in many countries of Europe, and pretty much all over the world.
Small mouth bass are native to streams and lakes in America from Lake Champlain west to the province of Manitoba in Canada. They range south to South Carolina, Mississippi and Arkansas.
Small mouth prefer clear cool waters, becoming a mountain stream fish in the South. Smallmouths, while not so adaptable to differing water and food conditions as Large mouths, have been pretty widely introduced to the cooler streams and lakes of America outside of those where they were indigenous.
Many anglers have trouble telling with certainty whether the fish they have caught are Large mouth or Small mouth bass. This is because many people try to tell the difference chiefly by color. As the color varies in different waters, all the way from silvery, through green and bronze to almost inky black, color just isn’t a reliable way to classify bass.
The surest way to help you with the problem of Large vs Small mouth bass, is by the “number of rows of scales on the cheek. The Large mouth has 10 rows. The Small mouth has 17 rows. The Large mouth has only 7 rows of scales on the body from the median line to the center of the back—the Small mouth has about 11 rows. The mouth of the Large mouth bass extends back of the eyes, while in the Small mouth bass the mouth extends only opposite the rear margin of the eye.
While the general color of the fish is not a good way to tell bass apart, the shape of the markings is. The Large mouth has a broad stripe that runs lengthwise on the sides of the body. The Small mouth has up-and-down dark bars. If you will remember these points of difference, you can definitely classify the bass you catch.