154 



Bashford Dean Memorial Volume 



b 



Text-figure 35. 



The head roof of Dmichthys intermedius Nwb. : 



A, as found; B, in reconstruction. 



a and b, clefts; c-c, axis of left socket; d-d, axis of right socket; 



c-d, movement axis of head; Ex, exterior corner of head; S}{. 



joint sockets. 



(American Museum No. 32.) 



out pointing to the importance of this fact for the reconstruction of the shape of the 

 head. The present writer in 1928 used this method in determining the curve of the head 

 roof in Heterostius and Homostius. Stetson (1930) also mentioned this fact. 



In Text'figure 35 A is shown the hind part of the head roof of Dinichthys inter^ 

 medius Nwb. (Am. Mus. Nat. Hist. No. 32) from behind. The roof is so strongly 

 flattened that it is nearly level above. Some large clefts (a and h) cross it and deform its 

 outline. The joint sockets are clearly seen on each side (S^). The dotted lines drawn 

 through their long axes (c-c and d-d) meet at an angle of nearly 100'. 



In reconstructing the real position of the joint sockets, we must bend the hind part 

 of the head so strongly that the long axes of both sockets are in the same horizontal line — 

 the movement axis of the head (Text-figures 35 B, c-d). Text-figure 35 B is a drawing of 

 such a reconstruction. It shows how strongly the head roof is curved. This curving 

 makes the head about 24 per cent narrower. The extreme side angles of the head roof 

 (Text-figures 12 and 13), formed partly of EB, PM and M, are now placed nearly vertically 

 (perhaps in reality they are still more vertical than shown on the drawing. Text-figure 

 35 B). We see now that the hinder consolidated arch of the head roof (Text-figure 13) 

 was strongly bent. This explains the clefts on compressed specimens (Text-figure 36). 

 The pressure has, of course, not only destroyed the hinder part of the head roof, but the 

 middle and front parts are also flattened and show many clefts and chinks. 



In the middle, as we know, the central part of the roof is thin (the roof of the neuro- 

 cranium), while the side parts are very thick (the side thickenings of the head roof). 

 Under pressure, the thick, curved side part was moved into a more horizontal position, 

 without being much broken. On the contrary the thin central part was split and bent 



