Chap. IX.] 
LOWER SILUEIAN TEILOBITES. 
205 
Trinucleus Murchisonii, Foss. 9. f. 7, together with the remarkable species T. 
Gibbsii, Foss. 10. f. 7, have already been quoted from the lowest beds (pp. 48, 51). 
T. fimbriatus, PI. IV. f. 7, and T. Lloydii, f. 6, are good indications of the Llan- 
deilo flags, for they occur in them only j while T. seticornis, Hisinger, a species 
found in Wales, Scotland, Ireland, and also in Sweden, is, on the contrary, ex- 
clusively a Caradoc form (see p. 69.) 
Fossils (47). 
Trinucleus concentricus : three specimens, distorted by Slaty Cleavage. 
This woodcut, in illustration of the various forms which a single species may assume 
under the influence of that change in the strata which is called slaty cleavage (see 
p. 32), represents a group of forms, apparently very dissimilar, but all of the same 
species, here given in their natural position on a fragment of slate. (Phillips, Report 
Brit. Assoc. vol. xii. pp. 60, 61.) 
Better specimens of some species of Trilobites having been found than those, 
which were collected at the time of the publication of the 1 Silurian System,' 
figures of them are given in the following woodcut, Foss. 48, namely Phacops 
conophthalmus, f. 3, and Ampyx (formerly Trinucleus) nudus, f. 7. Several 
species, not there described, have been since added to our lists, and a few of 
them are also here figured. Cybele verrucosa, f. 2, is one of these, and is a com- 
mon species in Britain and Sweden. C. rugosa, Portlock, Encrinurus baccatus of 
the same author, E. sexcostatus, Salter, Harpes Flanagani (Foss. 48. f. 4), and H. 
Dorani, Portl. (the latter both in Ireland and Wales), are all Caradoc or Bala 
species. Remopleurides dorso-spinifer, Foss. 48. f. 5, and three other species, 
Acidaspis bispinosa, f. 6, Cyphoniscus socialis, f. 8, and Cheirurus clavifrons, 
f. 1, all figured at p. 206, are common in Pembrokeshire and Ireland ; Cheirurus 
gelasinosus, Portlock, is now a well-known species in Scotland and North Ire- 
land. Lichas Hibernicus, from Tyrone, and Lichas laxatus, Foss. 46. f. 5, are 
examples of a highly complex genus not known in a complete form when my 
former work was printed. Illsenus Davisii, Foss. 46. f. 2, with II. Bowmanni, 
Salter, from Bala, and II. Murchisoni, Salt., from Carmarthenshire, are common 
Trilobites. Agnostus trinodus, Foss. 46. f. 6, is a Caradoc fossil ; A. Maccoyii, 
PI. III. f. 7, from Builth, is from the Llandeilo flags. A. pisiformis, Linn., the 
Swedish species, has been already quoted, p. 45. 
Some species of Acidaspis from Shropshire, and several fine forms from the 
Girvan district of Ayrshire have been figured by Professor Wyville Thom- 
son*, of Belfast, and Mr. Salter ; and there are numerous species and even 
genera yet undescribed. 
The minute Bivalved Crustacean of the Phyllopod tribe, Beyrichia complicata, 
Foss. 46. f. 7, occurs throughout the whole of the Lower Silurian region of 
Shropshire and Wales. Of this last-named genus several other forms are 
known : B. Barrandiana, Jones, is Lower Silurian ; B. Kloedeni, M'Coy, B. 
siliqua, Jones t, &c, are Upper Silurian species. The allied genus Primitia has 
* Quart. Journ. Greol. Soc. vol. xiii. p. 206. 
t Ann. & Mag. Nat. Hist. 1855, vol. xvi. pis. 5 & 6. 
