. The Bashford Dean memorial volume : archaic fishes. Fishes; Sharks; Fishes, Fossil. The Structure of Dinichthys 133 in any other animals. This circumstance must be remembered in comparing this figure with the Arthrodiran fragments. Median-Basal.—This plate (Text-figures 12, 13, 14, 15 MB, and 16) is the most massive one of the whole head roof. It is 9 cm. long, 15 cm. broad and 5 cm. thick;" and forms the central part of the posterior consolidated arch of the roof with its transverse commissure (tc) and double sockets (ds). In contradistinction to most of the other plates, MB can quite
. The Bashford Dean memorial volume : archaic fishes. Fishes; Sharks; Fishes, Fossil. The Structure of Dinichthys 133 in any other animals. This circumstance must be remembered in comparing this figure with the Arthrodiran fragments. Median-Basal.—This plate (Text-figures 12, 13, 14, 15 MB, and 16) is the most massive one of the whole head roof. It is 9 cm. long, 15 cm. broad and 5 cm. thick;" and forms the central part of the posterior consolidated arch of the roof with its transverse commissure (tc) and double sockets (ds). In contradistinction to most of the other plates, MB can quite often be found isolated. The limits between it and its neighboring plates are well developed. At the sides MB overlaps EB. In front it is overlapped by both C plates. Externo-Basal.—This plate (Text-figures 12, 13, 14 and 15 EB) forms the wings of the posterior consolidated arch. Along its posterior margin run the half-round thickenings (ht) on the ends of which the joint processes are placed (Jp). The upper, thinner part of EB forms the largest part of the bottom of the postero-lateral impression (PL). EB is overlapped by C, and partly over- lapped by M. However, the limits be- tween these three plates are difficult to see from the inside. On the outside of EB we find two branches of the sensory canals (Text- figure 12) which form a V-shaped figure. The point of this goes close to the joint socket, with which it is connected by a short canal (VII). One of the branches extends over on the M (VI). The other goes nearly to the edge of C (VIll). (In some specimens this branch runs over onto C). Marginal.—This plate (Text-fig- ures 12, 13, 14 and 15 M) is a solid long one, which together with EB and PM forms the postero-lateral wing of the head roof. Nearly along its center runs the posterior high ridge of the lateral head thickening (Rd). It forms the side wall Text-figure 16. of the postero-lateral impression (PL). median-basal plate of Dinichthys interrnedius Xhe M overlap
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Keywords: ., book, bookcentury1900, booksubjectfishes, booksubjectfishesfossil
