Geological Society of London. 103 
tained in the way of a subdivision of the group, and a 
paleontological distinction of importance has been indicated. 
They prove capable of division into two well-marked sections, 
viz.,a lower, of which Agnostus (probably the identical species 
described from the alum slates of Sweden), an Olenus, and 
Conocephalus occur along with the characteristic Lingule of 
the deposit; and an upper, where the same genera are ac- 
companied by a few Brachiopoda and Bryozoa, as in Bohemia. 
But whereas, in the latter country, no passage can be shewn 
of this fauna into the Silurian stage above, in Wales a pa- 
lzontological passage from the Lingula beds into the Bala or 
Llandeilo group appears to be indicated. This is marked by 
the association in the upper part of the igneous series of two 
large species of Olenus with Agnostus and Lingule, and 
with types unquestionably characteristic of the Llandeilo 
beds, such as Asaphus, Calymene, and Ogygia, and Grap- 
tolites of species undistinguishable from those of the Llan- 
deilo flags. 
The fourth and uppermost division of M. Barrande’s 
Lower Silurians is his “ Etage D;” strata chiefly composed 
of quartzites with schistose alternations. Cephalopoda re- 
presented by Orthoceras, Pteropoda by Conularia and Pu- 
giunculus, Heteropoda by Bellerophon, Gasteropoda by 
Pleurotomaria and Holopea, Acephala by Avicula and 
Nucula, Brachiopoda by Orbicula, Lingula, Spirifer, Lep- 
tena,and Terebratula ; also Crinoids, Cystideans, Starfishes, 
and a few Corals and Graptolites make up, with Trilobites, 
the fauna of this group in Bohemia. Trilobites and Cystideans 
prevail above all other forms, and it is in this zone that the 
former (and the latter probably also) attain their maximum. 
Of the four stages of Upper Silurians in Bohemia, the three 
lower divisions are typically calcareous, and the culminant 
Section schistose. The lowermost has a base consisting of 
traps alternating with black slates containing Graptolites, 
and including occasional concretionary limestone. It attains 
a thickness of not more than 900 feet, but has a fauna super- 
latively rich and prolific in fossil treasures. Between 500 
and 600 species of organic remains have been collected in 
this formation. In it is found the maximum number of 
