188 



Bashford Dean iS/lemorial Volume 



(we find a kind of analogy in the occipital double sockets pointed out in Gemundina by 

 Broili in 1930 and found in recent rays); it is incomprehensible in forms like Coccosteus or 

 Dinichthys, which, in all probability, could swim relatively very well. This is especially 

 true when we observe that in typical benthonic forms the neck joint was somewhat weak 

 (Heintz, 1929.1, .2), but in forms Hke Dinichthys and Coccosteus very strong. 



Text-figure 79. 

 The author's reconstruction of the armor of Dinichthys to show the mouth mechanism — the mouth shut. 



1, musculus levator capitis; II, musculus depressor capitis; 11/, musculus levator gnathalis; IV, musculus depressor gnathalis. 



2. The enormous keel on MD serves as an attachment for the muscles, which were 

 fastened by their fore part to the hind margin of MB. These muscles moved the head up 

 and down. Such strong muscles must have performed a movement of special importance 

 to the animal. 



3. The hinder part of the lower jaw, as mentioned before, is weakly built. It is 

 thin and narrow, without ridges or sockets for attachment of strong muscles. There is no 

 reason to suppose that it was consolidated with cartilage. 



4. The joint between the upper and lower jaws is very primitively built and, in 

 fact, can not be called a well developed joint. It has no condyle or fossa condyli. 



5. The front part of the lower jaw, on the contrary, is very strong. It is thick, 

 heavy and carries large teeth with distinct working marks. The hind part of the jaw and 

 the joint are too weakly built to give the heavy front part the necessary power to work. 



The whole mechanism functioned with the help of four pairs of muscles (Text-figures 

 79-81). Two pairs were attached to the head roof (I and 11); two pairs to the lower jaw 

 (HI and IV). The first strong pair, which we, like Adams (Text-figure 76) can call the 



