ASAPHUS. 151 



tail, and prominent behind, reaching seven eighths of the whole length ; it ends some- 

 what abruptly in a swelled tip. There are eighteen or twenty rings marked out on it, 

 not quite reaching the tip. The sides are convex, almost tumid at first, and ribbed by 

 twelve distinct raised ridges for about two thirds their width. These end rather abruptly, 

 and the concave limb is quite smooth and even, except for the imbricated lines of orna- 

 ment which cover the whole surface in one form or another. The lateral ribs are as 

 broad as the furrows between them, somewhat square in section, with tumid abrupt ends. 

 They are as numerous in young specimens (see fig. 12), and these are nearly as convex 

 as the older ones. 



The caudal fascia is broad, considerably indented by the axis, and concave, so as to 

 leave a space between it and the outer crust. The lines of growth are coarse, and rather 

 distant, obliquely set against the margin of the fascia (see fig. 10), not parallel to it. 



Of all the AsapJddce this is the most highly ornamented species. Our largest figured 

 specimen was, indeed, named, as a variety, ornatus by Sir R. I. Murchison (' Sil. Syst.,' 

 pi. XXV, fig. 1), but it is the normal condition of the old specimens, sometimes a foot long. 



The sculptured lines, which are veritable plicae or folds of the crust, are wavy and 

 interrupted, following a general curve all round the margin, but sinuous and inosculating 

 with each other. They follow the broad head-margin, and are concentric, fainter, and 

 closer round the forehead-lobe of the glabella ; but they are far stronger and shorter, and 

 form deep pits on the thorax-segments and tail, strongest on the axis of each, and occur only 

 on the prominent parts of the side-lobes, the hollows being nearly free from them. They 

 arch over the axis from side to side, almost obliterating the annuli of the tail-axis by their 

 strength ; while on the side-lobes they radiate from behind forwards, and decussate the 

 ridges strongly. They become transverse lines on the outer margins of the thoracic rings, 

 except in very old specimens (fig. 8), where they form pits and puncta to the very ends 

 of the pleurae. On the smooth concave limb of the tail they sweep forwards in sinuous 

 lines, strongly imbricated forwards, and cut the margin obliquely. 



On half-grown specimens they are much fainter, and, indeed, can only be rarely seen 

 in young specimens. 



The caudal fascia (fig. 10) has them distant, and branching, as it were, from an imagi- 

 nary line along its middle portion. But on the corresponding part beneath the thorax- 

 rings they are quite longitudinal instead of transverse. (See Decade 2, Geol. Survey, 

 pi. V, fig. 8.) 



There are few species to compare this fine fossil with, unless it be our next two 

 species. It is most nearly like the Asaplms Powisii, which occurs in Caradoc, not in 

 Llandeilo rocks. That species, however, shows no sculpture, and is, moreover, more 

 convex ; and it has very indistinct ribs on the tail, the axis of which is wide above, and 

 then suddenly contracted for the rest of its length. The species figured by Prof. Bur- 

 meister as A. tyr annus has, indeed (in his figure), a strong resemblance ; but that figure 

 is a mixture of two species, for the Professor has transferred the sculpture of the British 



