Most crystal filters are bandpass filters.  There are two types, one which consists of discreet resonators, as illustrated above, and the other, monolithic crystal filters which consist of acoustically coupled resonators, as illustrated on the next page.
	R. C. Smythe and R. S. Wagers, "Piezoelectric and Electromechanical Filters," in E. A. Gerber and A. Ballato, Precision Frequency Control, Vol. 1, pp. 185-269, Academic Press, 1985.
	R. G. Kinsman, Crystal Filters, John Wiley & Sons, 1987.