. Bulletin. Natural history; Natuurlijke historie. _, 0 Imm Fig. 2. Detail drawings of two cosmine margins, both from specimen MCZ 13350. Section A on the left shows an "unfinished margin" that is quite natural, with the cosmine and enameloid forming an essentially vertical face close by the opening to a lateral-line organ sunk within the spongiosa. Section B on the right is almost certainly also an "unfinished" margin, but it has also been eroded post-mortem as is shown by the fact that an undamaged pore-cavity, with infilling contents, is preserved just at the edge of the
. Bulletin. Natural history; Natuurlijke historie. _, 0 Imm Fig. 2. Detail drawings of two cosmine margins, both from specimen MCZ 13350. Section A on the left shows an "unfinished margin" that is quite natural, with the cosmine and enameloid forming an essentially vertical face close by the opening to a lateral-line organ sunk within the spongiosa. Section B on the right is almost certainly also an "unfinished" margin, but it has also been eroded post-mortem as is shown by the fact that an undamaged pore-cavity, with infilling contents, is preserved just at the edge of the fossil. The later erosion of the margin probably resulted from natural weathering of the fossil. d = dentine; e = enameloid; / = lateral-line canal; pc = pore-cavity; s = spongiosa. The pulp-cavity is formed in three parts—a central broad trunk, a crown of rapidly tapering broad extensions from the trunk, and a branching system of fine tubules that extends through the dentine and into the basal part of the enameloid layer. Virtually all the dentine tubules radiate from the crown region but the walls of the trunk region may occasionally be seen to be perforated by a series of very short tubules that seem to be dentine tubules (Fig. 1). It may be noted that not all the dentinal units contain only a single pulp-cavity. Occasionally there arise from the vascular bed of the spongiosa a series of two or three connected trunks from which dentine tubules radiate. A similar situation has been noted in other osteolepids by Gross (1956: , fig. 31A). The dentine itself shows signs of internal differentiation (see p. 28) and even under low magnification, thin-sections may show evidence of concentric laminations, particularly at the edge of cosmine sheets. These details will be considered more fully below. The dimensions of the pore-canal system in Ectosteorhachis nitidus fit generally with those given for other cosmine systems (as in the work of Gross, 1956) with the exception that t
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Keywords: ., bookcentury1900, bookcollectionbiodiv, booksubjectnaturalhistory
