Chap. IX.] 
LOWER SILURIAN TRILOBITES. 
203 
species, were it not that the glabella has only two pairs of furrows and is long 
and urceolate. The British species is a good representative of Barrande's 
Fossils (45). Lower Silurian Trilobites op the ' Primordial Zone ' of Wales. 
i 
1. Paradoxides Davidis, Salter. 2. Olenus micrurus, Salter. 3. Olenus cataractes, 
Salter. 4. Agnostus princeps, Salter. 5. Angelina Sedgwickii, Salter. 6. Ampyx 
pr£enuntius, Salter. 7. Cheirurus Frederici, Salter, 8. Conocoryphe depressa, Salter. 
9. Asaphus (Isotelus) Homfrayii, Salter. 
Bohemian type. Angelina Sedgwickii, fig. 5, Ampyx praenuntius, fig. 6, Chei- 
rurus Frederici, fig. 7, and Asaphus (Isotelus) Homfrayii, fig. 8, are all exclusively 
Upper Tremadoc species *. 
The genera of Trilobites peculiar to the Lower Silurian, not only in this 
country, but on the Continent and in America, are : — Olenus, Conocoryphe, 
Agnostus, Paradoxides, Cybele, Trinucleus, Ogygia, Asaphus, Remopleurides, 
and the trilobed forms of Illamus, the first four being principally (though not 
wholly, except Paradoxides) confined to the lowest division or Lingula-flags. 
On the other hand, the genera Ampyx, Calymene, Lichas, Proetus, Homa- 
lonotus, Cheirurus, Encrinurus, Bronteus, and that division of Illaenus which 
I still believe to be a true genus t (Bumastus, Murch.), are found both in the 
Lower and Upper Silurian. Mr. Salter has reminded me, further, that there is 
scarcely one genus of the upper division which had not previously existed in 
the earlier period. 
Of these there is perhaps no one species which has a greater vertical range, 
* The reader who wishes to study these and phical Society, 
other Trilobites must take in hand Mr. Salter's t The pygidium is simple, not trilobed as in 
masterly ' Monograph of the British Trilobites,' most species of Illaenus. 
now in course of publication by the Palseontogra- 
