BRACHYASPIS. 



167 



Head rather shorter than semicircular, gently convex ; the angles rounded, but rather 

 produced and incurved. The space between the eyes equal to the length of the head, 

 the large, curved, semicircular cornese being placed at one third from the base, about their 

 own length distant from it ; the eye-lobe horizontal, flattened above, and surrounded by 

 the very convex lentiferous surface. The glabella quite obsolete, only marked by a deep 

 punctation below the eye. The facial suture nearly straight above the eye, curving 

 gently out, and cutting the front margin, along which it runs. Below the eye it runs out- 

 wards much beyond the eye about halfway along the cheek, and parallel to the posterior 

 margin. On the underside of the head a narrow, convex, incurved margin shows the deep 

 ■narrow pit above the angle for the reception of the pleurse in rolling, and in front has a 

 wide flat hypostome, divided by no vertical suture as in Isotelus, and showing a rather 

 narrow base of attachment for the labrum, which is not yet known. 



Of the body-rings we have only five, and these have a very broad axis, much wider 

 than the pleurae, and only divided from them by a shallow sulcus. They are much curved 

 forward at their rounded ends. The fulcrum lies near the axis, about one foui-th out. 



The tail (/. arcuatus, Portlock) is wider than a semicircle. The upper angles are 

 much bent down for the facet. The axis, marked out at its origin by two deep impres- 

 sions, is at this part rather wider than the side-lobes. 

 But from this point backwards it is not indicated, except 

 by a slight prominence at the apex, which occurs at 

 three-fourths the length of the tail. A broad shallow 

 furrow beneath the fulcrum is all the marking that shows 

 on the smooth convex sides. Caudal fascia concave, so 

 narrow that its edge is not indented by the point of the 

 axis ; it is strongly lineated, the lines abutting sharply 

 against the inner margin. /. intennedius, of Portlock, 

 was formerly quoted by me wrongly as a synonym. But 

 General Portlock erred in comparing this species with 

 A. tyrannus, which it does not in the least resemble. 



But, if compared with the recently published Asaphus 

 lavigatus of Angelin, the resemblance is so close that, 

 were it not for considerable differences in the proportions 

 of the head, and especially in the course of the facial 

 suture beneath the eye, I should have combined that 

 species vrith ours. They are, however, clearly distinct. We must include A. Icevifjatus 

 in the same subgenus, and I give a figure of that species, which may serve to illustrate 

 the subgenus Brachyaspis. 



Fig. 36. 



Asajphus Brachyaspis") lavigaius, 

 Angelin, Lower Silurian, Sweden. 



Prom the ' Palseontologia Suecica,' 

 pi. xxix, fig. 1. (The thorax is 

 imaginary.) 



