22 
William Patten. 
Holaspis tlie presence of a semicircular sériés of minute grooves or pits. They difter, 
however, from tliose of Tremataspis iu their somewhat indefinite lineal arrangement, witli tlie 
grooves sometimes running a cross the sériés instead of parallel with it. Lankester s 
figures of Pteraspis (PI. VI figs. 1 and G) show two lines of dots tliat may perliaps represent 
the marginal and the posterior dorsal line of Tremataspis. 
In Pterichthys and Bothriolepis , Traquair has described what lie calls «a lateral line 
System» consisting of a sériés of grooves «which are apt to he and hâve often been 
mistaken for sutures». Traquair states, p. 488, that «they» (the lines) «do not occur 
on the inferior surface of the boues, and their connection with a similar groove running 
along each side of the hody araply demonstrates their true nature.» 
It seems to me that we must await further evidence before definitely accepting the 
lines of surface markiugs in Tremataspis , Pteraspis and Pterichthys as evidence of the 
presence of lateral line organs, directly homologous with those of modem vertebrates. The 
absence of markiugs on the internai surface of the Shell does not preclude the possibility 
that the grooves in question are fused sutures; and it is not at ail certain that the longi¬ 
tudinal groove in Pterichthys is comparable with the lateral line on the trunk of true ver¬ 
tebrates. 
There is however considérable resemblance between the lines of dots and daslies of 
Tremataspis and the grooves of Pterichthys. The circum-orbital and the marginal lines of 
the former being clearly the same as the so called trunk line and the circum- 
orbital line of Pterichthys. There is even in Pterichthys , the slight backward bend or 
loop at the anterior end of the circum-orbital line so strikingly shown in Tremataspis. 
The transverse and the posterior dorsal lines of Tremataspis do not appear to be repre- 
sented in Pterichthys. 
An examination of the two splendid lieads of Tolypaspis preserved in the Petersburg 
Academy shows the presence of a Y-shaped ridge on the dorsal shield that appears to in- 
dicate the presence of a circum-orbital line similar to that of Tremataspis. This ridge is 
shown in Rohon’s figures’ 93 (PI. I. fig. 45), but is not otherwise referred to. In taking 
an impression of one of these specimens, a part of the shell was removed showing the 
presence of a median pit on the inner surface of the shell in the median eye région. It is 
thus evident that the shield in question is comparable with the dorsal shield of Pteraspis, 
not with the ventral one as Schmidt supposed. Rohon appears to bave entertained the 
same view as Schmidt in regard to it. Oui* interprétation is further confirmed by the 
presence of the marginal notch and the circum-orbital line mentioned above. 
v 
