The present paper describes the mode of occurrence of remains of Plesiosaurs and Ichtyosaurs in upper horizons of the Upper Jurassic bituminous shale of the Lower Volga at the Savelyevka shale mine, 35 km southwest of Pugachev, Saratov Region. The remains of marine reptiles are imbedded in a series alternsting dark gray marly and bituminous clays. The lower and larger part of the series belongs to the Perisphinctes panderi zone; the upper part, with one working horizon of combistible shale, belongs to the virgatites virgatus zone. Besides reptile bones, the clays and shales contain a multitude of remains of marine invertebrates: ammonites, brachiopods, pelecypods and echinoderms. During the period that the mine has been in operation, from 1931 to 1940, there have been found about 20 different remains of Ichtyosauria and Sauropterygia, b-longing chiefly to the genus Ophthalrnosfurus of the former and to the Pliosauridae of the latter order. Altogether there have been found about twice as many remains of Ichtyosauria as of Sauropterygia. Of particular interest is the almost complete skeleton of a large Pliosaur found in 1933 in mine No. 1. This skeleton has been mounted, and is now on exhibit in the Pugachev museum. Also of interest is the finding of an almost complete skeleton of a very large Ichtyosaur (not preserved, due to mining operations), a cervical verebra of a Plesiosaur of the Colymbosaurus type and, lasly, fragments of the lower jaw of a gigantic Pliosaur having a skull about 3 meters long.
During the developing of the skeleton of the Pliosaur there were found near the roof of its mouth ribs of a large reptile, and in the region of its stomach remains of a large fish and a large number of hooks from the arms of decapods, and also small (3–4 mm.) gastroliths. In the region of the posterior part of the body there were found several Crustaceans (Glyphea) and a large number of Cypridina. Moreover, on the surface of the concretions encasing the skeleton there was a membrane (up to 1 cm thick) of a black, retinous substance, presumably a product of the decomposition of the corpse of tie Pliosaur. The cephalopod hooks and the fish remains signify that these animals served as food for the PIiosaur.
The Lower Volgen Sea, in which dwelt the Pliosaurs and Ichtyosaurs in contrast to the biassie bay of Holzmaden, was a normally saline busin with a normal gas regime. It was rather shallow, on its bottom a rich flora developed, giving rise to the bituminous shale, and a rich fauna dwelt in its waters.