From Holocron - Star Wars Combine
|Average Height||2 meters |
|Skin color||pale pink |
|Hair color||Red, blonde, brown, black (usually turning gray or white with age) |
|Distinctions||Cone-like skulls |
|Known Members||List of known Cereans|
Biology and Appearance
Cereans are tall, gaunt humanoids with an enlarged skull that contains a very big brain. They are a wise and perceptive race whose binary intellectual capabilities allow them to look at an issue from many different angles, making them excellent problem solvers.
Cereans were a sophisticated and cultured humanoid mammalian species that hailed from the planet Cerea. They had tall tapering heads, which housed large binary brains, enabling them to focus on many things at the same time. Aside from this unique feature, Cereans were physically similar to Humans, although they possessed an extra heart, which supplied extra blood circulation to support their brains. 
Cerean males aged more quickly than the females, who had similar lifespans to Humans. Thus, there were fewer males than females. Polygamous marriage was a necessity in order for the species to survive. Each male usually had one primary "bond-wife", and between four and ten "honor-wives". 
Their enlarged skulls, extending up to twenty centimeters above their foreheads, housed complex binary brains, provided with sufficient blood by an extra heart in their heads. The binary structure of Cerean thinking helped them to ponder two sides of an issue at once. It also enabled them to process information and solve problems rapidly. Because of their thoughtful nature, they tended to be calm, rational, and analytical, preferring peaceful philosophies and a lifestyle which worked in harmony with nature. Though the quick-thinking Cereans had equally quick reflexes, they were commonly not as well coordinated as Humans. Because of the weight of their enlarged skulls, Cereans often had back problems. 
Society and Culture
While they are renowned for their intellect, their capabilities as leaders in battle go almost unrecognized by scholars. They are docile by nature, but when confronted with life-or-death decisions, they become fierce and fearless individuals, inspiring these traits in those under their command when leading a group in battle.
They are very ecologically-minded beings, as their homeworld of Cerea relies on a very fragile balance of flora and fauna to maintain its natural cycles and continue sustaining life. This oneness with nature has proven itself time and again as a quality that helps make them excellent survivors in nearly any planet's wilderness. Cereans throughout the galaxy have made names for themselves as excellent scholars due to their superior logic, excellent ability to retain knowledge, and innate problem-solving skills, making their intellects highly valued by educational institutions everywhere.
Cereans developed a low-tech society on their homeworld, and preferred to live in isolation from the wider galaxy. Many Cereans used specially-forged Kasha crystals as a meditational tool. By focusing one's thoughts while in contact with such crystals, distractions were eliminated, creating an exceptional meditation environment. Cerean Jedi sometimes incorporated these crystals into their lightsabers, providing great focus, even during intense physical combat. 
References:  - http://starwars.wikia.com/wiki/Cerean