The Primitive Fishes 289 



the seas of eastern North America, Brazil, and India at 

 least. 



Other Cestracionts, like Palaeobates, Palaeospinax, 

 Strophodiis, and Bdellodus, derived doubtless from modifi- 

 cation and adaptation of freshwater palaeozoic forms that 

 lived on in scant numbers, and as yet unknown to science, 

 appear alongside or after the latter, and in the same beds. 

 An abundant literature might be correlated and cited to 

 prove equally the contemporaneous relation and the fresh- 

 water habitat of these, notably of Hybodus RndAcrodus, 

 the two commonest and most widely dispersed genera. 



Thus L. Richardson, in describing the Rhaetic rocks of 

 Monmouthshire (275:374) and of Glamorganshire (pp. 

 385,391) speaks of a bone bed in each, and says: "A fine 

 piece of this fish-bed . . contained in great abundance, 

 the teeth of Acrodus miimniis, Gyrolepis alberti (?), 

 Sargodon tomiciis, and Lepidotus ( ?) less commonly of 

 Hybodus minor and H. cloacinus." In subjacent beds he 

 found Lycopodites and abundance of Estheria, as well as 

 remains of the amphibian Mastodonsaurus. In a still later 

 paper (2/^:385) he plots out inch by inch the strata of 

 the Keuper, Rhaetic, and Lower Lias. In the Lower 

 Rhaetic he describes a set of four marl deposits — the Sully 

 beds — in which shells of the marine Ostraea\ Aviciila, 

 and Pecten are mixed with Gyrolepis, Sargodon, and Acro- 

 dus. These suggest either that a constant land oscillation 

 was proceeding, with a mixture of either living or dead 

 marine and freshwater types, or the above shells were 

 washed out and redeposited with the fishes. A thin layer 

 of shale separated these from a five-inch bone bed made up 

 of remains of Acrodus minimus, Saurichthys acuminatus, 

 Sargodon tomicus, Hybodus minor, H. cloacinus and frag- 

 ments of bone. Still higher up vertebrae of Plesiosaurus 

 and Glyptolepis alberti were added. 



In a paper by Brodie on the Upper Keuper (2/7:43: 

 540) he tells of finding together Palaeoniscus, Semionotus, 

 remains of Cestraciont sharks, footprints of labyrintho- 

 donts, plants like Foltzia and Carpolithus, also marls with 

 Estheria. Wills and Smith, for the Upper Keuper of 

 Central England, emphasize (2/5:461) a bone bed with 



