Twelve species of pelecypods representing the subfamilies: Pycnodonteinae, Exogyrinae and Ostreinae are described. The growth changes in Pycnodonte (Phygraea) vesicularis and in Gryphaeostrea vomer are reported. The "fingerprint shell structure", has been found ort the shell of P. (Phygraea) vesicularis, and it is interpretrd as the remain of conchiolihe membrane in the subnacreous layer. In earlier stages of the Upper Cretaceous in, the Middle Vistula region the ostreids dominate, While in the later ones brachiopods and belemnites are more aboundant.