On the Structure and Affinities of Palaeodiscus and Agelacrinus . unted clockwise II, III, IV, V. Viewed externally the ambulacra of Lepidodiscus pileus are seen tobe roofed over by an alternating series of plates which are shapedlike a bent finger, fig. 9. These do not completely enclose the groove,there being small interspaces between each covering plate. Bothlongitudinal and transverse section show that these plates also formthe sides of the groove. There is no trace of any separate sideplates. We may therefore call this upper series of plates side-covering plates. There are often slight in
On the Structure and Affinities of Palaeodiscus and Agelacrinus . unted clockwise II, III, IV, V. Viewed externally the ambulacra of Lepidodiscus pileus are seen tobe roofed over by an alternating series of plates which are shapedlike a bent finger, fig. 9. These do not completely enclose the groove,there being small interspaces between each covering plate. Bothlongitudinal and transverse section show that these plates also formthe sides of the groove. There is no trace of any separate sideplates. We may therefore call this upper series of plates side-covering plates. There are often slight interspaces between them 40 Mr. W. K. Spencer. On the Structure and [Mar. 22, throughout most of their depth. An examination of the series ofphotographs as also the wax models show that no pores are presentleading into the interior of the test. These plates were on an average13 mm. in thickness, the plates covering the mouth are merelyenlarged side covering plates. They occupy the angles of thoseinter-radii which border the mouth region. These inter-radii are not. Text I^iqb. 9, 10, 11, 12.—Progressive views of reconstructed wax model ofLepidodiscus {Agelacrinus) ^ileus \ I, II, III, IV, V = ambulacra , side-covering plates; , mouth plate of anal inter-radins , mouth corner plate ; , flooring plates. By error in the figures,the amhulacra have heen numbered V, I, II, III, IV instead ofI, II, III, IV, V. Fig-. —Outermost view. five in number but three, namely those between II and III, III andlY, IV and V. This is because a secondary triradiate symmetry hasbeen imposed upon the primitive pentamerous symmetry of this genus,vide infra. Two of the mouth-covering plates are of equal size. They aresmaller than the third, which occupies the angle of the anal inter-radius. The ambulacral groove is floored by a series of single oblong plates,which stretch across the groove, and show no trace of median suture orpore, figs. 10,11. They do not correspond in nu
Size: 1866px × 1339px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectproceed, bookyear1904
