There's an old joke that Toyota Prius product planners must have heard. It goes like this:

A crime has been committed. The police are seeking a suspect who has managed to escape. He is described as a short-statured psychic. A story in the next day's paper is headlined: "Small medium at large."

You can almost hear Prius product planners exclaim, "That gives me an idea!"

And, thus, for 2012 the Prius hybrid family grows from a single hatchback to three body styles — small, medium and large.

The "large" is the Prius V, a new wagon version of the familiar Prius hatchback. The hatch is the "medium," which soon will be available as a plug-in hybrid in addition to its standard form. The 'small," unveiled last month at the North American International Auto Show in Detroit, is the Prius c.

The "c" stands for "city." This tiniest Prius is an urban runabout that shrinks Toyota's Hybrid Synergy Drive system down to a size that fits comfortably in a vehicle that, compared to the Prius hatchback, is 19 inches shorter, 2 inches narrower and 542 pounds lighter, all riding a wheelbase that's half a foot shorter. Also, c's roof is 2 inches nearer the tarmac.

Nonetheless, the little guy, which shares its platform and suspension with the Toyota Yaris, manages to incorporate into its drivetrain all the Prius hybrid hardware: four-cylinder gasoline engine, continuously variable (CVT) automatic transmission, two electric motors (one of which acts as a starter/generator) and a nickel-metal hydride battery pack. It's just that all these elements are smaller than those of a standard Prius.

The gasoline engine in c, for example, is a 1.5-liter, 73-hp affair, which compares to the 1.8-liter, 98-hp gas engine in the Prius and Prius V. Likewise, c's battery pack is a 144v nickel-metal hydride bundle of 120 cells compared to the 201v, 168-cell pack of a standard Prius.

In c, total system power, including battery and electric motor assistance, is 99 hp. It's 134 in a standard Prius.

Finally, c offers just three drive modes — Normal, ECO and EV — compared to four (all of the above, plus Power) in Prius and Prius V.

The ECO mode reduces throttle response and dials back air-conditioning function to enhance fuel economy. The EV mode is a pure electric mode good for about a mile at speeds under 25 mph — looking for a space in a parking garage, for example.

Normal mode is...uh...well...you know.

In c, it all adds up to an EPA mileage rating of 53 city/46 hwy/50 combined. That works out to 2 better in town than a regular Prius but 2 worse on the interstate. The vehicles share a 50-mpg combined rating. Still, c can claim the highest city mpg rating of any gasoline-sipping passenger vehicle without a plug.

Inside, the five-passenger c provides more room than you have a right to expect from a subcompact hatchback, including more than 17 cubic feet of rear-seats-up cargo room. In fact, the EPA will officially rate the subcompact c as a compact due to its overall interior room, said Moe Durand, a Toyota spokesman.

Of course, few cars in the 21st century arrive in showrooms without a bevy of available infotainment goodies, and Prius c is no exception.

Available in One, Two, Three and Four trim levels, even the base C boasts a standard 3.5-inch multi-information display, Bluetooth hands-free phone capability and a USB port with iPod connectivity.

Move up to Three and Four trims, and c throws in Entune, an exotic infotainment system with, among other things, a 6.1-inch touch screen, satellite radio receiver, Pandora internet radio, voice-command navigation and an interactive feature that allows the driver to order everything from flowers to movie tickets to pizzas, along with the option of calling up real-time traffic, weather, fuel prices, sports, and stocks.

Starting at $19,710 for a One and topping out at $23,990 for a loaded Four, both including destination charge, c is the gateway to the Prius family.

It arrives in showrooms next month.