The Matamata is one of the largest freshwater turtles.  An adult age turtle could reach a shell size of 18 inches.  Its flat head is connected to a long neck which presents many protuberances, warts and ridges.  Its scutes have a conical shape and they are determine by well formed symmetrical rings.  The mouth is wide and the snout is long.  Matamata's eyes are very small and they are located by the snout.
The Carapace and neck color vary from a dark brown to a mahogany; while the plastron has a salmon color.  With the time, the salmon color changes on the plastron to yellows and browns.  The throat on the young has a reddish brown color and eventually will change to a tan brown. (Matamata) 

Matamatas are well known for looking their food during the night on the island of Trinidad.  Among their diet is found: fish, amphibians, freshwater crustaceans, possibly birds and small mammals that get into the water.  The Matamata hunting technique is unique among the chelonians.  While opening their mouth and expanding their throat, the Matamata extends the head up and catch their prey.  These  movements, made at the same time, create a suction action that draws the prey to their long and  expanded throat; the pray is swallowed and the water is expelled out. (Grzimek'sAnimal Life Encyclopedia)

The Matamata of South America is a very interesting and probably the most diverse  in form of all the turtles.  Their flat head seems triangular because of extensions of the skin found in both sides; a flexible snorkel is located at the end of the head.  Three rows of large humps cross their flat back.  The posterior part of their eyes are lined with a crystalline wall (a tapetum lucidum) which makes the light reflect; a similar characteristic is seen in crocodiles and other nocturnal reptiles.  (Reptiles of the World).  "A full-grown Matamata with a shell 18 inches long appeals to the human mind more like a vision of a disordered dream than a living reptile." (Grzimek'sAnimal Life Encyclopedia, p.119)

Personal Observations:

The Matamata is one of nature's unique species that stands in a genus by itself.  It is a fascinating animal that displays numerous exotic features.  One is their peculiar technique used  for hunting their prey.  They actually suck the fishes into their throats, and at the same time they expelled the water out. The Matamata is a turtle but also it has many properties or characteristics that have been compare to those of crocodiles.  If we take a close  look to this turtle we will find many features similar to the features of a crocodile. 

-Espenshade,William-"Matamata". 
www.tortoise.org/archives/matamata.html

-Raymond, Ditmas-"Reptiles of the World"-1998 P.52 

-Grzimek,Bernhard-Grzimek'sAnimal Life Encyclopedia 

  Reptiles-Vol #6-Van Nostrand Reinhold Company  Publisher, 
  1975,Pag.118-120.