Catalogue of the fossil fishes in the British Museum (Natural History) .. . m and proportions of the anterior shield havealready been determined by Lankester (fig. 25), and the fossils underdiscussion are quite similar to those previously studied. The absenceof posteriorly prolonged cornua is distinctly shown; there is thewell-defined high posterior ridge behind the postorbital valley,*and the usual three layers entering into the constitution of the shielare readily distinguishable. There is also no trace of sensorycanals. 186 OSTEOSTRACI. The superficial ornamentation is not very satisfactori
Catalogue of the fossil fishes in the British Museum (Natural History) .. . m and proportions of the anterior shield havealready been determined by Lankester (fig. 25), and the fossils underdiscussion are quite similar to those previously studied. The absenceof posteriorly prolonged cornua is distinctly shown; there is thewell-defined high posterior ridge behind the postorbital valley,*and the usual three layers entering into the constitution of the shielare readily distinguishable. There is also no trace of sensorycanals. 186 OSTEOSTRACI. The superficial ornamentation is not very satisfactorily exhibited,but one specimen (P. 6109) shows an impression of the externalsurface, represented of four times the natural size in PL X. fig. 3;and this evidently conforms to the type described and figured byLankester in the fossils from the Ludlow Tilestones, namedC. ornatus by lilgerton (fig. 25, A). Lankesters determination of theidentity of the latter form with C. murchisoni is thus confirmed. A novel point of much general interest is elucidated by the middle Fig. Cephalaspis murckisoni, Eg.—Outline of shield, and portion of ornament muchmagnified (A). After Lankester. layer of the shield, which is well preserved in several already demonstrated by Huxley and Lankester, this layer isdivided into a number of distinct polygonal areas, by a system ofreticulate, branching vascular canals ; and the present specimensprove distinctly that it extends backwards as a pair of postero-lateral flaps beyond the rest of the shield. Such an extensionis shown in PL X. fig. 1, a?, in the individuals numbered I. and the large group (P. 6023) mentioned below. The outer layer isbroken away, so that direct continuity can be observed between theappendage and the middle layer, and the precise shape of most ofthe areas or plates is distinguishable. As far as the posterior ex-tremity of the shield the outer lateral margin is apparently undividedby vascular channels, and the a
Size: 2052px × 1217px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorbritishmuseumnaturalh, bookcentury1800, bookdecade1880
