The Structure of Dinichthys 



121 



Text-figure 8. 



Bryant's reconstruction of Dinichthys mirabilis 



Huss. & Br. (1918). 



AL, antero-lateral; C, central; EO, external-occipital; IL, 

 intero-lateral; M, marginal; Md, mandible; MO, median- 

 occipital; Mx, maxillary; P, pineal; PrMx, pre-maxillary ; 

 PrO, pre-orbital; PtO, post-orbital; R, rostral; SO, sub- 

 orbital. 

 (After the present author's sketch made in the 

 Buffalo Museum.) 



little and the postero-lateral was included in 

 the carapace, but its size and position are 

 wrong. 



5. The condyle and the fossa condyli 

 are not placed horizontally. This makes 

 movement of the head absolutely impossible. 



6. The sub-orbital is not connected 

 with the pre-orbital. 



7. The maxilla and pre-maxilla are not 

 correctly placed in relation to each other and 

 to the sub-orbital. 



8. The position of the mandible is in- 

 correct. It is placed too low down and comes 

 in contact with the clavicular. 



The next figure of a reconstruction of 

 Dinichthys is found in Hussakol and Bryant's 

 "Catalogue of the Fo6sil Fishes in the Museum 

 of the Buffalo Society of Natural Sciences" 

 (1918). The present writer was able to study 

 this reconstruction (made by Bryantj during 



his visit to the Buffalo Museum. It is a reconstruction of Dinichthys magmficus n.sp. 

 (Text-figure 8). It can only be regarded as an unsatisfactory attempt, and gives an in- 

 correct picture of Dinichthys. I will merely point out here that the whole head carapace 

 is too flat, the median part of the head is depressed instead of being arched, the sub-orbital 

 is wrong in its outlines and position, and the mandible is too strongly curved and is 

 fixed to the lower part of the antero-lateral (clavicular). Besides this reconstruction, 

 there is exhibited in the Buffalo Museum, a plaster model of the fore part of Dinichthys 

 mirahilis in natural size. This model, which also includes the body carapace, shows still 

 more mistakes. It is enough to state that the position of the head shield in relation to the 

 body carapace makes all movement between head and body totally impossible. 



In the American Museum of Natural History there is a model of Dinichthys inter- 

 medius made by Hussakof. Here the whole fish is shown in natural size. This model is 

 much better than the one in the Buffalo Museum, but here also the head is too flat. An- 

 other mistake worth mentioning is that the distance between the right and left parts ot 

 the upper and lower jaws is too great. 



In 1919, Adams gave a sketch (Text-figure 76) of Dinichthys in his book "A Memoir 

 on the Phylogeny of the Jaw Muscles in Recent and Fossil Vertebrates." He has here briefly 

 given the first description of a new plate placed at the posterior corner of the mandible. 

 This plate shows a joint impression and, according to Adams, by its aid the mandible was 

 suspended to the sub-orbital. We shall return to Adams' new theory of jaw movement in 

 the Arthrodira in another part of this work. 



