Note on Microdiscus speciosus.

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Abstract
IN mv original description of this interesting Trilobite (thisJOUl'l1u( August, 1873) it is stated that the thonlx is composed of four equal segments.The description, in so far as relates to this part of the animal organi.zation,was drawn up from the study of a single specimen, showing the head, thorax and pygidium in nearly their natural positi.ons,and apparently offering deciRive testimony as to the true number of body-rings.Somew hat more than a year ago, however, I obtained from the Troy beds another specimen, of almost precisely the same dimensions, showing clearly but three segments in the thorax; anel, subsequently, a milch larger specimen showing the same number.ThiR led me to re-examine, more critically, tbe specimen employed in the original description, when it was found that the bead had slipped slightly forward, and that what I had regarded as the first pleura (all of the pleurre of one side, as well as one-half of the head, being enveloped in the matrix) was a fragment of some foreign body that had fallen into the gap thus made.The deception, in the first instance, was rendered all tile more complete from the fact that, by the displacement of the head alluded to, the al,ticulal' fold of the fil'st body-ring, which is ordinal'ily wholly hidden from view b.y the backward prolongal.ion of the glabella, was exposed, thus making it very good case fOl' a fourth segment.I now consider it celtaiu that this species has never more than three body-rings.I have in my collection a small rolled-up specimen showing the extl'emities of but two body•segments, and I was at fil'st led to think it possible that we had iu this species an example of the metamorphoses of 'rrilobites, concerning which Barmnde has taught us so much.But as I have observed since this specimen was obtained, an individual of even smaller size, with three perfectly f()rmed body-segments, this notion is without foundation at the p,'esent time.I should here also add th:1 t the last body-
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Authors S. W. Ford
Journal american journal of science
Year 1877
DOI
10.2475/ajs.s3-13.74.141
URL
https://doi.org/10.2475/ajs.s3-13.74.141
Keywords Keywords not found

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