The Structure of Dinichthys 



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limited by a very large and heavy process, "processus glenoidalis" (pg), which forms the 

 immediate prolongation of the lower consolidated arch of the head (Text'figure 12). Its 

 front is roundish, and oblong in form, with a plane surface (Text-figure 70B). On the 

 underside it is semicircular in section and is gradually attenuated towards the point 

 (Text'figure 70B and C). On its inner side we find a small process, the lower joint 

 process (Ijp), placed nearly opposite the upper joint process. The lower margin of EB 

 is divided from the processus glenoidalis by a deep cleft (cl). The whole arrangement is 

 very strong and massive. 



Corresponding with the fossa glenoidalis on EB, is the strongly developed "condylus 

 glenoidalis" (Jaekel) on ADL (Text-figures 71 A, B, C; and 72A, B). It is composed of 

 the real condylus (eg) and a broad strong and massive ridge (rg), serving as a support. 

 The condyle is long, roundish in the front part (a), posteriorly it takes on a more conical 

 outline and its hind corner (b) is relatively narrow. The supporting massive ridge 

 (rg) has a broad hinder part which gradually goes over into the surface of ADL 

 (Text-figures 7lB; 72 A and B). Toward the condyle it rises and becomes thinner. On 

 both sides of the condyle it is relatively very thin, thus forming two well-marked impres- 

 sions (see section — Text-figure 73). The impression on the upper side of the condyle 

 is especially strongly developed and forms a real fossa. We shall call it the upper joint 

 fossa (ujf). On the inner surface of ADL immediately under the condyle ridge, is a well 

 marked, roundish place {psg). Corresponding with what is found in other Arthrodira, 



Text-figure 70. 

 The joint socket on the hind margin of the externo-basal plate : A, from outside; B, from behind; 



C, from inside. 



cl, cleft between processus glenoidalis and hind margin on £B; /g, fossa glenoidalis; Ijp, lower joint process; Jig, processus 



glenoidalis; ujp, upper joint process. 



