. The Bashford Dean memorial volume : archaic fishes. Fishes; Sharks; Fishes, Fossil. 134 Bashford Dean Memorial Volume characteristic for the M on all Arthrodira. The center of this figure is placed in the ossifi- cation center of the plate. One branch goes up to the PtO (IV), the other (V) down and outward to the external angle (Ex) of the roof, and the third (VI) runs over on EB where it continues into the previously mentioned canal. Post-Marginal.—This plate (Text-figures 12, 13, 14, 15 PM, 1? and 18; Plate III, figure 7) is one which has never before been observed in Dinichthys. It is a l
. The Bashford Dean memorial volume : archaic fishes. Fishes; Sharks; Fishes, Fossil. 134 Bashford Dean Memorial Volume characteristic for the M on all Arthrodira. The center of this figure is placed in the ossifi- cation center of the plate. One branch goes up to the PtO (IV), the other (V) down and outward to the external angle (Ex) of the roof, and the third (VI) runs over on EB where it continues into the previously mentioned canal. Post-Marginal.—This plate (Text-figures 12, 13, 14, 15 PM, 1? and 18; Plate III, figure 7) is one which has never before been observed in Dinichthys. It is a little triangular plate that forms the extreme point of the external angle and gives to it its char- acteristic sharp-pointed outline. Like a little hollow cap, PM is fitted on to the extreme parts of M and EB and in this manner connects them firmly together. On the inside PM greatly overlaps M and EB; on the outside more moderately. The suture on the outside is complicated, as is seen from Text-figures 12, 17, 18 and Plate III, figure 7- PM is the plate of the whole head roof most loosely joined to its neighboring plates, and therefore is often found isolated. For the same reason the otherwise complete head roof often lacks PM only. In other Arthrodira PM has been found and figured before. Thus Traquair in 1894, in describing a head of Phlyctaenaspis acadica Wt. from Canada, figured a new plate which formed the extreme corner of the roof and was placed behind M and EB. He called it "; Considering its position, relation to other plates, and the fact that we find on it a continuation of the sensory canal from M, this plate corresponds with our post- marginal. Jaekel in his papers on Pholidosteus (1907) gives some reconstructions of this form. Here we find a small plate between M, EB, and PSO. This plate, considering its position and relation to other plates, must have been the same as PM in Dinichthys. Jaekel has never described it nor given it a special name.
Size: 2368px × 1055px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., book, bookcentury1900, booksubjectfishes, booksubjectfishesfossil
