. The Bashford Dean memorial volume : archaic fishes. Fishes; Sharks; Fishes, Fossil. The Structure of Dinichthys 141. away from it. It curves forward and continues onto the handle (Text-figures 22 and 23 Rj) where it runs nearly to the point of the tongue-shaped part. In the beginning this ridge is low but rises quickly and reaches its greatest height about the curving point (Text- figures 22 and 23 y). It keeps this height to the end. As seen from Text-figures 22 and 23, it runs in a half-circle around the orbital impression and forms its lower wall. Another ridge begins at about the middle
. The Bashford Dean memorial volume : archaic fishes. Fishes; Sharks; Fishes, Fossil. The Structure of Dinichthys 141. away from it. It curves forward and continues onto the handle (Text-figures 22 and 23 Rj) where it runs nearly to the point of the tongue-shaped part. In the beginning this ridge is low but rises quickly and reaches its greatest height about the curving point (Text- figures 22 and 23 y). It keeps this height to the end. As seen from Text-figures 22 and 23, it runs in a half-circle around the orbital impression and forms its lower wall. Another ridge begins at about the middle of the hind margin (Text-figures 22 and 23 ). Quickly rising, it runs forward to the curving point of the first ridge (Text-figures 22 and 23 y) where it makes a sharp curve, and forms a high crest (Text-figures 22 and 23 Pr). From this point the tongue- shaped part of the handle begins. As we know, the tongue-shaped part is placed behind the outside of SO and thus its in- ner surface is nearly on the high plane of the ridges. After a sharp curve, this ridge runs along the middle of the tongue- shaped part, but now as quite a low edge (Text-figures 22 and 23 R4). Between the orbital wall and this edge runs a groove (Text-figure 22 gr). It is deeper and narrower at its beginning, but becomes flatter and broader forward. A very clear, deep impression (Text-fig- ures 22 and 23 ip), located between the curving point of both ridges, connects it with the posterior part of SO. As we see, the structure of SO is very complicated and difficult to describe. It can be better understood by studying Text-figures 21, 22 and 23. We may point out furthermore that the outline of SO is rather variable in different species . of Dmichthys. Thus in Dmichthys terrelli Nwb. its blade is relatively long and narrow, and the handle shorter; in Dinichthys interynedius Nwb., on the contrary, the blade is broad and relatively short, but the handle is strong and massive (Text-figure 24). Post-Nasal.—Thi
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