(1) Female Mask Type....
Binhari (also pronounced bimbari) describes a fish with heavy growth on the gill covers. It takes its name from a hairstyle popular in Japan in the 1700s, in which a woman's side locks were puffed out by placing a whalebone support inside them
(2) Pocket Towel Type...
A tokin is a kind of round cap worn by certain religious practitioners in medieval Japan; it looks a little like a pillbox hat. Fish with pronounced growth on the top of the head are described as tokingashira, or "cap head." The presence of this tokin in young fish is believed to mark them as eventually growing to have the ideal, allround head growth called shishigashira.
(3) Dragon Head Type.....
A dragon head (tatsugashira) Ranchu has imposing growth between the eyes, projecting forward symmetrically in two rounded shapes resembling traditional depictions of dragons in Chinese and Japanese art.
(4) The Lion Head Type...... 
Finally, the shishigashira, or lion head, takes its name from the shishi, the mythical lion-dog of China and Japan (which looks a little like a giant Pekinese). A fish with heavy growth starting from the bottom and covering the entire head is called a shishigashira.
From Mr Geert Coopen's article...The Standard of Perfection of the Ranchu and under the description of "Head of a Ranchu"
The head should be long, broad and rectangular. The skull should be deep. The distance between the eyes or mehaba should be as broad as possible. The distance between the eyes and the mouth or mesaki should be as long as possible. The eyes should be small and set in the right position; neither too high nor too much forward. The hood or wen is a thickening of the skin on the head. Thanks to the hood the head gets a nice rectangular shape. A good Ranchu has a hood that develops on the entire head, on the gills and around the eyes.
In eXtreamRanchu under "Appreciation"..... another description of "Head of a Ranchu"
Perhaps the most prominent feature of the Ranchu is the head (kashira). There must be sufficient space between the eyes, and from the eyes to the front of the head, and the gill cover should be "deep" -that is, extend quite far toward the tail. Headgrowth should seem to start from the bottom of the gill cover and move upward. Fish with broad foreheads and square noses generally produce better headgrowth.
References:
http://www.ranchubrotherhood.be/nl/the-standard-of-perfection-of-the-ranchu-english-32.htm
http://www.extreamranchu.com/mc/scoop_detail.php?a_id=59&ag_id=1
http://tw.myblog.yahoo.com/jw!0CMlSHOBEhh85tKl/article?mid=5453&prev=7580&next=1073&l=f&fid=6
The pictures of the four different type of ranchu head was copied from a bro blogger as above. I cannot remember which Japanese Master put up the original pictures...any hobbyist that can enlighten will be greatly appreciated.
