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 A HISTORY OF BEDFORDSHIRE Two reptiles have also been identified from the Chalk of the county, namely the common Cretaceous fish-lizard Ichthyosaurus campy- lodon, of which an imperfect jaw is known from the Totternhoe Stone at Chalton ; and the large short-necked pliosaurian Po/yptychodon interruptus, of which the large fluted conical teeth occur in the Chalk-marl. I am informed that Mr. W. Ransom of Hitchin has in his collec- tion remains of the cave-lion (Fe/is leo spelced) and wild horse (Equus caballus fossilis) from Langford. Mr. J. S. Elliott has shown me a tooth of the above-mentioned saurian Ichthyosaurus campylodon and another of a shark from the Cam- bridge Greensand of Henlow ; and the coprolite-pits in that formation have doubtless yielded many other vertebrate remains similar to those from Cambridgeshire. Among the reptilian remains from the Potton Sands is included the base of a dinosaurian skull, described by Professor H. G. Seeley 1 as Craterosaurus pottonensis ; it is too imperfect to afford decisive evidence as to the affinity of the animal to which it belonged. Bones and teeth of the great three-toed bipedal reptile of the Wealden, the Iguanodon, occur not uncommonly in these deposits ; as well as those of its carnivorous cousin Megalosaurus. Crocodiles are represented by the huge Dacosaurus (or Geosaurus) maximus, of which the conical and carinated teeth have been washed out of the Kimeridge Clay and reburied in these deposits. Remains belonging to both groups of the great marine saurians characteristic of the Secondary period are also common in the Potton Sands. Of the ichthyosaurs, or group in which the head is large, the neck short, the eyes furnished with a ring of bones, and the bones of the paddles articulated together in a pavement-like manner, the Cambridge Museum possesses a fine series of remains from these deposits. Of the second group, or plesiosaurs, in which the neck is often long and the bones of the paddles are of more normal type, several forms are known. Among the long-necked and small-headed types are Colymbosaurus trochanterics, C. brachistospondylus and Murcenosaurus trun- cates, all of which occur typically in the Kimeridge Clay. From the same formation are derived the large triangular teeth of Pliosaurus — a short-necked and large-headed member of the group — which are of such common occurrence in the Potton beds. Scales, spines, palates and teeth of several kinds of Jurassic fishes are likewise met with in the Potton beds. Among these it will suffice to mention the large button-like teeth and polished rhomboidal scales of the Kimeridgian ganoid Lepidotus maximus, the palates of the pycno- dont ganoid Gyrodus cuvieri, the elongated crushing teeth of the shark Hybodus obtusus, derived from the Kimeridge or Oxford Clay, and the dental plates of Ischyodus townsendi, a species belonging to the same group as the modern chimera, whose remains occur typically in the Portland Limestone of Wiltshire and Dorsetshire. 1 Quart. Jour,,. Geo/. Soc. xxx. 183 (1874). 34