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Bashford Dean Memorial Volume 



Dinichthys is a nearly triangular plate with the hind lower part strongly curved 

 upward (Sp). It is thickened along the lower margin and thin elsewhere. On the 

 outside, the lower margin (Im) is sharply separated from the upper part. In the 

 hind part it is strongly curved forward and upward. The upper part is clearly 

 divided in two, with a border running from the upper angle of IL (ua) in an 

 arch-shaped curve downward nearly to the middle of the lower margin. The part between 

 this edge and the upper margin of IL is striped with some fine impressions, all beginning 

 from the upper angle, running in an arch shape downward to the lower margin, and divid- 

 ing the surface of the plate into long narrow 

 strips. The most remarkable feature is that 

 this part is ornamented by fine, very dense, 

 small tubercles. It is the only part of the 

 whole armor of Dinichthys, where such or- 

 namentation is found. In Plate VIII, figure 

 22, a part of IL is reproduced three times en- 

 larged to show the ornamentation more 

 clearly. We shall come back to this remark- 

 able structure later. 



The other part is very thin and smooth. 

 It is, following the curved lower margin of 

 the plate, strongly curved itself in the hind 

 lower portion. Its margin, between the 

 upper angle (ua) and the lower thickened 

 portion (Irn), is very thin and nearly always 

 broken, which makes it difficult to determine its outline precisely. On the inside, IL is 

 smoother. The thick lower margin is a little concave and its surface is rough. The 

 upper part shows a distinctly overlapping margin (ov) on its hind corner. This part of IL 

 covers the fore part of the hind wing of AL. 



Spinal. — This plate is the second which aids in the union of the ventral and dorsal 

 shields. Claypole early indicated its presence in Dinichthys (1893.1). In recent times 

 Abel (1919) has pointed out that in Dinichthys "kurzie Rudimente der Spinale ist vor- 

 handen." But its real form and attachment to the other body plates have never been 

 described. 



In other Arthrodira it was mentioned for the first time by Newberry, as the spine 

 in his new genus Acanthaspis (1870, 1875) which he placed in Cephalaspida. Von Koenen 

 in a series of papers on the placoderms from the north German Upper Devonian (1876, 

 1880, 1883, 1886, 1890.1, .2 and 1895) described a new Coccosteus — Coccosteus hir}{ensis 

 v. K. — with a long spine. He regards this spine as homologous with the movable appendix 

 in Asterolepida known under the name ''Ruderorgan.'' From von Koenen's drawing it is 

 clear that, as a matter of fact, his "Ruderorgan" corresponds to our spinal. In a discussion 

 with von Koenen, Traquair (1890.5) asserted that in Coccosteus decipiens Ag. the spinal 



Text-figure 63. 



Crushed head and body carapace of PhoUdosteun 



sp. Jk. 



(Sketch made by the author in 1927 from Jaekel's original 



material. ) 



(I), left; (r), right A Vi and IL. 



