@book{19214,
	author = {Twenhofel, William H. and Shrock, Robert R.},
	title = {Principles of invertebrate paleontology /},
	publisher = {McGraw-Hill,},
	year = {1953.},
	series = {McGraw-Hill series in geology},
	address = {New York :},
	edition = {2d ed.}
}