362 



THE OSTRACODERMS. 



Fig. 238 shows a photograph of a head in which the plates are retained in their 

 proper place. 



Sections of the whole buckler show that the lateral margins of the upper and 

 lower shields were united by bony trabeculae, and that two plate-like entapophyses 

 projected from the inner surface of the dorsal shield, that probably served for the 

 attachment of muscles. (Fig. 236, r.) 



The lateral line organs consist of short, shallow grooves separate in the younger 

 specimens, but united into longer grooves in the older ones. There is a circum- 

 orbital, lateral, occipital, and a posterior dorsal line. Short, sensory grooves 

 occur on some of the isolated oral plates. 



Appendages. Associated with the remains are certain plates that have the 

 same peculiar texture as the shields, and which undoubtedly represent portions 

 of the armored appendages. A complete distal joint has been found. (Fig. 241.) 







241. , D, E, Distal joint of a cephalic appendage of Tremataspis; C, haemal; D, median; E, neural 

 surface; F, appendage of some unknown animal associated with the remains of Trematapsis. It consists of five 

 or more joints. A part of the large distal joint has broken off, exposing the impression of the outer surface, that 

 was marked by faint transverse ridges. Superficially, the shell covering the joints resembles that of Tremataspis. 

 Seen from the inside. X 9. 



It is oblong, with a broad, partly membranous, posterior surface, a scalloped 

 anterior edge, and an articular process at its proximal end. A convex, heart- 

 shaped plate was also found that represents the dorsal part of the proximal 

 joint. (Fig. 240.) It was attached by a narrow roughened collar probably to 

 the larger anterior marginal incision. In each of the three known specimens of 

 this plate the polished outer surface is cut by a semicircular groove, showing 

 where it struck against the margin of the shield in the forward and backward 

 movement of the arms. (Fig. 240.) There is no place where such plates could 

 be attached to the body or head except in the larger anterior incisions. They 

 fit in this position fairly well and in this position they agree with the corre- 

 sponding parts of the cephalic appendages of Bothriolepis. 



The smaller, more posterior incisions or openings may have served for the 



