. Bulletin of the British Museum (Natural History), Geology. DOWNTONIAN OSTRACODERM SCLERODUS 3 and finally, whether the generic name should be changed to Eukeraspis. By the turn of the century the consensus seemed to be that there was one species, that it was a cephalaspid fish closely related to Thyestes and that the original material described by Agassiz represented the denticulated cornua and should go under the name of Eukeraspis. Woodward (1917) considerably clarified the situation by following through his earlier suspi- cion (1891: 195) and a suggestion by Priem (1910: 5) that Plectrodu
. Bulletin of the British Museum (Natural History), Geology. DOWNTONIAN OSTRACODERM SCLERODUS 3 and finally, whether the generic name should be changed to Eukeraspis. By the turn of the century the consensus seemed to be that there was one species, that it was a cephalaspid fish closely related to Thyestes and that the original material described by Agassiz represented the denticulated cornua and should go under the name of Eukeraspis. Woodward (1917) considerably clarified the situation by following through his earlier suspi- cion (1891: 195) and a suggestion by Priem (1910: 5) that Plectrodus mirabilis and P. pleiopristis represented the dentigerous jaws of ischnacanthid acanthodians. This is the current status of Plectrodus (Denison 1979: 41). Thus, Sclerodus pustuliferus remains the only cephalaspid material described by Agassiz in Murchison's The Silurian System. The change of generic name to Eukeraspis is unnecessary (see also Stensio 1932: 175, footnote). Subsequent work* on Sclerodus is chiefly that of Stensio (1932), who has provided the most complete description, Denison (1951a, b) and Janvier (1975). These authors differ in their interpretations of the 'cornua' and sensory fields and their ideas are discussed in the relevant descriptive sections below. A summary of the differing ideas of the morphology is provided in Fig. 1. Lankester 1870 Stensio 1932 cells'. lateral field cornua. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original British Museum (Natural History). London : BM(NH)
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