Northern Right Whale Dolphin (Lissodelphis borealis)
For orientation, the head with blowhole is to the right. Note that the back is entirely smooth and lacks a dorsal fin. This characteristic led to both the name of their genus (lisso means smooth) and their common name (right whales also lack dorsal fins). They're the only dolphin or porpoise in this area without a dorsal fin.
Here's a view of most of the animal out of the water (below). Adults reach lengths of 2-3 meters (6.5-10 feet). Note the fusiform shape (spindle-shaped, or broader in the center and tapering at both ends).
They're black above, with variable amounts of white below, especially on the chest and at the tip of the lower jaw. The next photo shows a right whale dolphin on its side underwater. You can see the broad white patch on the chest (and a hint of white at the tip of the jaw at the right side of the photo).
The white on the ventral side continues to the flukes. The small flukes (~1 foot across) also show white patches on the underside.
Northern Right Whale Dolphins are streamlined fast swimmers. They've been clocked traveling at ~17 mph and at bursts up to ~30 mph (Allen, Mortenson, and Webb 2011).
This is one of my favorite cetaceans to encounter on pelagic trips. They're often in groups, and you can see them leaping out of the water from a great distance. Highly sociable and often associated with other cetaceans (dolphins and whales), when Pacific White-sided Dolphins are bow-riding, Northern Right Whale Dolphins often join in. All of these photos are from 2 September 2012.