The Structure of Dinichthys 131 



limit and become gradually thinner toward the margin (Text-figure 14). Their fore part 

 (FP), placed approximately between the nostril impressions and the pre-orbital process, 

 is strongly thickened. We find here, along the margin, the different sockets, crests and 

 impressions (ss, pns), which serve to attach the plates of the side of the head (P?v[and 

 SO) to the head roof. Between the pre- and post-orbital processes is a moderate impres- 

 sion for the eyeball (Ei). It is sharply limited (OrL) forwards, but gradually disappears 

 ■ at the back. On the margin immediately behind the post-orbital process, is a shallow notch 

 for the reception of the upper corner of the SO plate {SoT^) (Claypole, 1892. 2). 



The inner limit of the side thickenings not far behind the post-orbital process be- 

 comes very massive, with many small crests, ridges and impressions. From the middle of 

 this part rises a long, thick, angular process {?ip) which bends over the central part of 

 the head roof. These processes extend inward from both sides and so surround a tri- 

 angular room where the neurocranium lies. Therefore we will call them the neurocranial 

 processes. 



A little behind these processes the side thickenings begin to narrow, thus running 

 nearly parallel to the inner limit of the posterior consolidated part of the head roof. In 

 this part the side thickenings are changed to the before mentioned narrow high ridge (Rd) 

 with a sharp edge. This ridge rises bow-shaped and gradually descends to the point of 

 the external angle of the roof. 



In this manner, the head roof of Dinichthys is consolidated with the help of several 

 thickenings: first, the postero-median (PC A), then, the symmetrical antero-laterals (LCP). 

 These two sets of thickenings are connected with one another with the help of two 

 "bridges" (CR) which form a massive, flat thickening with an oblong impression at the 

 top (ti). They go from the front of the posterior consolidated arch obliquely forward 

 and come in contact with the side thickenings not far behind the neurocranial processes. 

 Together with the hinder consolidated arch they form an X-shaped figure. 



With the help of this system of thickenings the remaining thin part of the roof is 

 divided into three parts: the central (CP) which is placed between the side thickenings, 

 and the twopostero-laterals (PL) placed between the hind part of the side thickenings 

 (Rd) and the hind consolidated arch of the roof (PC A). 



The central part begins at the transverse limit of the median part of the hind con- 

 solidated arch (trl). This limit is very sharp and steep, so that the thickened part even 

 overhangs the thin central part, making a kind of cavity (Text-figure 14, cv). On the 

 other hand, the limit between the connecting bridges (CR) and the thin central part (CP) 

 is not so sharply marked. At both sides the central part is, as mentioned before, sharply 

 limited by the side thickenings. 



Nearly on the level of the neurocranial processes, the central part is divided into two 

 parts by the pineal plate (P). This is a rather thick, oblong, triangular-shaped plate, which 

 continues to the rostral part of the head (R). The thin central part, divided into two, 

 continues upward as two branches (Br). They curve a little outward and end as a well 

 marked socket behind the orbital impressions (ts). This central, thin part of the roof, 



