40 
The thorax is made up of eleven segments ; the axis is convex and clearly 
separated from the pleurae by well-marked furrows ; each of the two ends 
of its rings has a projecting tubercle; the pleurae are granulose and rather 
strongly curved upon themselves at about half their length. The pygidium 
is sub-triangular, often ending in a more or less long process ; the axis is 
made up of from twenty-three to thirty , segments, the medium portion of 
which is usually defaced, and thus forms a smooth longitudinal band on which 
are placed five or six small projecting pointed tubercles. The lateral lobes 
are divided into a number of ribs, varying in different specimens from eight 
to ten, separated from one another by well-marked furrows ; the direction of 
these ribs is more inclined to the axis as they approach towards the posterior 
extremity of the animal. 
Horizon and Localities. — In England and Sweden this species is 
characteristic of the Upper Silurian, and is found in the Llandovery and in 
the Wenlock limestone, as well as in the limestone of Gothland. I am not 
certain that the specimens of Hncrinurus occurring in great abundance in 
the Lower Silurian of the Galway Listrict in Ireland, which have a great 
resemblance to this species, and which M‘Ooy described as Hncrinurus Stokesi^ 
are really identical with it, as Salter thinks. 
Among the numerous specimens collected in Australia, only two belong 
to Hncrinurus pimctatus. One, the pygidium of which only is preserved, 
comes from the Yass Listrict, and occurs in a quartzose rock, coloured red by 
oxide of iron ; it is associated with Hentamerus ohlongus, Sowerby, and Cyatho- 
j)hy lliim articulahmi, Wahlenberg, the presence of which proves the geological 
horizon ; the other, almost complete, and wanting only a small part of the 
head, has been found at Luntroon in a slightly yellow and little friable 
schistose argillaceous rock. 
2. Enceinurus Baeeandei, L. G. de Koninck. 
PI. I, fig. 8. 
Though I know only the head and pygidium of this species, these two 
parts are sufficiently characteristic to enable me to readily separate it from 
H. punctatus and variola7'is, the two species which are most like it. 
It must be noted that M‘Coy abandons these names in his “British Pateozoio Fossils,” p. 158, while 
holding that the species differs from that described by Fletcher and Salter under the name of E. pimctatus, and 
that it is the same as that described by Wahlenberg. I am of opinion that the contrary is the case. 
