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Bashford Dean Memorial Volume 



Text-figure 40. 

 The position of the sub-orbital plate in relation to the head roof: A, in crushed specimens; 



B, in reconstruction. 



it extends nearly downward. Its side margin touches the front part of PT^ without any 

 strong connection. R and P?v[ together limit the nasal openings. The post-nasal fills 

 the recess between SO, PrO and R. With its hinder margin it is strongly connected 

 to SO, and its upper margin comes in contact with PrO. 



The contact between the blade of SO and the side margin of the head roof is not easy 

 to reconstruct. They were only connected by means of skin, ligament, or perhaps cartilage. 

 No sockets or crests are observable either on the edge of the blade ot SO or on the side 

 margin of the head roof. It is interesting to point out- that, in forms from Wildungen, SO 

 and PSO are very intimately connected with the head roof and are nearly always found 

 together with it. But in Dinichthys the only certain attachment point between these two 

 parts is a little notch behind the post-orbital process, where the upper corner of the blade 

 of SO fits in. Thus the orbital openings are encircled by a very solid bony ring composed 

 of SO, PrO and PtO. 



Sclerotic Ring. — This is fitted into this bony ring. It is composed, as in all other 

 Arthrodira, of four separate bones.' In Dinichthys, as in Coccosteus, these elements 

 are rarely found. In other forms from the Cleveland shale (e.g. Solenosteus) they 

 are very common. Also, in all forms from Wildungen the sclerotic rings are always 

 preserved. The sclerotic bones in Dinichthys (Plate III, figure 5) are relatively very broad. 

 The opening for the eye is therefore small. Text-figure 41 gives the picture of a sclerotic 



"Dean (1901.1) described the sclerotic ring of Stenosteus as composed of five plates. Probably this is a mistake. 



