. The Bashford Dean memorial volume : archaic fishes. Fishes; Sharks; Fishes, Fossil. 200 Bashford Dean Memorial Volume Head foof. very near the median line, immediately in front of the ventral shield (Text-figure 87). As Broili pointed out, very probably these arches are a part of the visceral skeleton. Together with the majority of scientists, the present writer is of the opinion that the gill apparatus in the Arthrodira was placed under the head shield and that the split be- tween PSO and AL is the gill opening. It is hardly possible that the body carapace served ,-----.^^ as a protector fo
. The Bashford Dean memorial volume : archaic fishes. Fishes; Sharks; Fishes, Fossil. 200 Bashford Dean Memorial Volume Head foof. very near the median line, immediately in front of the ventral shield (Text-figure 87). As Broili pointed out, very probably these arches are a part of the visceral skeleton. Together with the majority of scientists, the present writer is of the opinion that the gill apparatus in the Arthrodira was placed under the head shield and that the split be- tween PSO and AL is the gill opening. It is hardly possible that the body carapace served ,-----.^^ as a protector for the branchial region (cor- /' "v responding to the opercular region in other fishes). In forms like Acanthaspida from Spitsbergen (Heintz , .2) the body carapace is very long, making it unlikely that the gill openings would have been placed be- hind the body carapace, since they would have been pushed unnaturally far backward. The same would occur in Coccosteus angus' tus, described by Bryant (1929). On the con- trary, in forms like Heterostius the whole body carapace is shortened and thickened, and there is no room for'gills behind it (Heintz ). It has been remarked that there is too little room for the gill apparatus underneath the head shield. If we compare the heads of the Arthrodira with the heads of other fossil and recent fishes, it is easily seen that in the majority of forms the place for the branchial apparatus is not larger than that in the Ar- throdira. In fact, behind the posterior part of SO and PSO and the front part of AL and IL, there is sufficient room to place an effective branchial apparatus. Another circumstance makes the location of the gills in this region very probable. The surface of IL, as mentioned before, is the only place in the whole of Dinichthys, showing a distinctly superficial ornamentation. This ornamentation has been previously described (See Plate VIII, figure 22). We must suppose that it is a preserved skin part which cov
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