Catalogue of the fossil fishes in the British Museum (Natural History) .. . the latter author. Fig. 18 shows the dorsal contour ofthe shield, with its parts indicated by the lettering. The severalprominences of the hinder border are the lateral cornua {p. c), themedian spine (p. s.), and the broad median production of the shield,with its sharp angles (p. «.). Each orbit has a surrounding rim(o. ?.), extended in front into a small antarbital prominence (*) ;and between the eyes is an elongated interorbital prominence (\evidently hollow, and homologous with the pit in the pineal plateof t
Catalogue of the fossil fishes in the British Museum (Natural History) .. . the latter author. Fig. 18 shows the dorsal contour ofthe shield, with its parts indicated by the lettering. The severalprominences of the hinder border are the lateral cornua {p. c), themedian spine (p. s.), and the broad median production of the shield,with its sharp angles (p. «.). Each orbit has a surrounding rim(o. ?.), extended in front into a small antarbital prominence (*) ;and between the eyes is an elongated interorbital prominence (\evidently hollow, and homologous with the pit in the pineal plateof the Antiarcha (see p. 210). Immediately in advance of the latteron the under surface of the shield is a small, short, narrow medianseptum. Between the antorbital prominences and this septum isthe pair of small antorbital fossae (a. /.) exposed only when thesubstance of the shield is removed; and another great superficialfossa (p. o. v.) extends from a ridge or groove (i. g.) joining the hinderborders of the orbits to the origin of the median ridge (p. r,) which Pig. Cephalaspis.—Diagram of inferior aspect of shield, showinginferior rim ; after Lankester. terminates in the posterior spine. Inexplicable concavities imme-diately beneath the cranial roof near the rostrum are named marginalcells (m. c), these being more extensively developed round the rim inEukeraspis (fig. 27, p. 194); and when the fossil is so preserved as toshow the contour of some of the originally soft parts, the cast of a 179 pair of great rounded lobes, meeting in the middle line, is con-spicuous in advance of the orbital region. As shown from beneath(fig. 19), the margin of the shield is reflexed inwards to form aflattened and ornamented inferior rim, wider behind than in front;and, as proved by transverse sections (fig. 20), the inner border of
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Keywords: ., bookauthorbritishmuseumnaturalh, bookcentury1800, bookdecade1880
