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Bashford Dean Memorial Volume 



MB 



Text-figure 42. 

 A total reconstruction of the head of Dinichthys seen from the side. 



ASG, antero-supra-gnathal; £B, externo-basal; C, central; IG, infero-gnathal; M, marginal; MB, median-basal; Nr, nostril; P, 

 pineal; PM, post-marginal; Pl^, post-nasal; PSG, postero-supra-gnathal; PrO, pre-orbital; PSO, post-sub-orbital; PtO, post-orbital; 



R, rostral; SO, sub-orbital. 



The whole body carapace can be divided into a dorsal shield; a ventral shield; and 

 the plates connecting these two parts. 



THE DORSAL SHIELD 



The dorsal shield is composed of nine plates, namely; the single median-dorsal, 

 the rights and lefts of the antero-dorso'lateral, of the postero-dorso-lateral, and of the 

 antero-lateral and postero'lateral. 



Median-Dorsal. — This plate (Text-figures 44 and 45) is the largest in the whole 

 armor of Diyiichthys. In a large specimen of Dinichthys terrelli Nwb. it may measure along 

 the median line (without the process) up to 50 cm.; across the broadest part 65 cm., and 

 nearly 10 cm. in the thickest part. Its form and proportions are known from figures and 

 descriptions in older works (Newberry, Claypole, Eastman, Dean, Hussakof). I shall 

 therefore here point out only some especially significant facts. 



