ILLJENITS BALCLATCHIENSIS. 57 



have been liitlierto regarded as only of a varietal importance or due to age, than to 

 associate them with a species already sufficiently overburdened in this respect. 

 Such is the case with these Balclatchie specimens, which seem allied to, though 

 not identical with, the typical /. bowmani. It is on the strength of the well- 

 preserved pygidia, not of the imperfect head-shields, which in their poor state are 

 practically indistinguishable from /. bowmani, that this species is separated. 



Tn Mrs. Gray's collection from Balclatchie, however, there is one small specimen 

 of this species showing the whole individual, but slightly crushed and broken; 

 and another specimen with five thoracic segments attached to a typical pygidium. 

 We are thus enabled to describe to some extent the characters of the head and thorax. 

 The thorax in this example only possesses eight segments, whereas /. bowmani 

 has nine, but the smaller number may be due to immaturity. The axis is 

 wide, subcylindrical, tapering very gently to the pygidium, and is not so wide 

 as the pleuroe. The pleurae consist of a flattened inner horizontal straight portion 

 and an outer extra-fulcral portion of about equal length, bent strongly downwards 

 and less strongly backwards. The fulcrum is situated at about half the length of 

 the pleuras and at a distance from the axial furrow equal to two thirds (or rather 

 more) the width of the axis. 



The head is not very well preserved in the entire individual from Balclatchie, 

 but another from Balclatchie and a still more perfect example from Ardmillan 

 enable me to give a nearly complete description. The head-shield is semi-oval, 

 about tAvice as broad as long, convex, and more or less strongly bent down in front. 

 The glabella is about half the length of the head-shield and less than one third its 

 width, gently convex, and defined by well-marked axial furrows, nearly straight 

 and parallel and deepening posteriori}'. The fixed cheeks are gently convex and 

 nearly as wide as the glabella. The eye-lobes are small, prominent, projecting 

 laterally, and situated at about one third the length of the head from the posterior 

 margin. A narrow occipital segment is visible at the base of the glabella and 

 on the fixed cheeks in the Ardmillan cast. The facial sutures have their anterior 

 branches from the eyes to the front margin nearly parallel, curving convergent lv 

 inwards near the front margin. Behind the eyes the posterior branches bend 

 outwards sharply, to cut the posterior margin at about 60°. The free cheeks are 

 well preserved in the Ardmillan specimen, and are long, narrow, and pointed 

 anteriorly at about 20° — 30°; their length is more than twice their breadth, and 

 they are about two thirds the width of the fixed cheeks. The genal angles are 

 very widely rounded off, and the posterior and lateral margins form one continuous 

 gentle curve. The surface of the head-shield is seen (in the Balclatchie specimen) 

 to be punctate like the pygidium. 



Affinities. — This species has been confused with /. bowmani, which, indeed, it 

 resembles in general characters, particularly in the shape of the pygidium, but it 

 differs from typical examples in the pygidium in the degree of definition of the 



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