Geological magazine . idth (transverse measurement) is 61 diameter is towards the posterior part of the opening. Thegreatest length (antero-posterior measurement) is 4-4 mm,, this being H. L. Haivkins—Buccal Plates in Echinocorys. 223 absolutely on the long axis of the test. The area of the peristome isnot flat, and hardly in any part parallel with the adoral surface of thetest. The most deeply sunken part is at the anterior margin, and,with the rest of the test, the edge of the peristome curves sharply uptowards the plastron from about the region of its greatest feature is
Geological magazine . idth (transverse measurement) is 61 diameter is towards the posterior part of the opening. Thegreatest length (antero-posterior measurement) is 4-4 mm,, this being H. L. Haivkins—Buccal Plates in Echinocorys. 223 absolutely on the long axis of the test. The area of the peristome isnot flat, and hardly in any part parallel with the adoral surface of thetest. The most deeply sunken part is at the anterior margin, and,with the rest of the test, the edge of the peristome curves sharply uptowards the plastron from about the region of its greatest feature is indicated in Fig. 1, b. The actual margin of theperistome is visible in the specimen under description only in itsposterior part, being overlapped anteriorly by the peristomial is probably due to the warping of the membrane on which theseplates were fixed. In ordinary specimens, however, the margin iscompletely smooth, without any trace of sockets for the articulationof the peristomial plates. o °o= o o. o :o Fig. 1. Plating of the buccal membrane in Echinocorys. A, camera lucidadrawing, x about 65 ; B, sectional view, diagrammatic. The Peristomial Plates. The plates of the peristomial membraneare preserved in situ, the slight displacements that they show beingprobably due to the inward contraction of the membrane after are polygonal, mostly pentagonal, in shape, and seem to beexceedingly thin. The surface of all of them is finely shagreened,in contrast to that of the coronal plates, which are almost smoothbetween the miliaries. The outer ring in contact with the margin of the peristome consistsof eleven plates of considerable size and very regularly sutures between them are approximately continuous with theperradial and interradial sutures of the test. The four largest platesof this cycle are towards the anterior edge, and correspond in positionto the anterior radius and the two antero-lateral interradii. Theyare pentagonal, and, while op
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Keywords: ., bookcentury1800, bookdecade1860, booksubjectgeology, bookyear1864
