XXXll DESCRIPTIVE REMARKS. 
Theea ; such as a thick shell showing lines of sept at regular intervals, 
which are independent of the fine transverse striz with which the 
surface is marked, these characters being identical with that of Ortho- 
ceras. 
The small tapering and tubular shell, ornamented at regular 
intervals with rings, Tentaculites Anglicus, Pl. x., fig. 3, is remarkably 
frequent in some beds of the Caradoc sandstone, particularly at the 
locality from which the examples figured were obtained, in a buff- 
coloured sandstone from Cheney-Longville, Shropshire ; it is also plen- 
tiful in Llandovery strata. 
Minute bivalved Crustacea belonging to the Ostracoda, such as 
those figured on Plate xii. Cytheropsis umbonata, fig. 1, and Primitia 
Maccoyti, fig. 2, are not uncommon in some of the Caradoc deposits ; 
the latter species being remarkably abundant in the limestone of this 
age at the Chair of Kildare. 
Beyrichia, fig. 3, and Agnostus, fig.4, are other small crustaceans ; the 
former, a bivalved Phyllopod, the latter, one of the rudimentary forms of 
the extinct group of Trilobites, a class of fossils largely represented in 
these rocks; some of the most common species being figured on the 
same Plate, such as Jilenus Bowmanni, fig. 5; very plentiful in the Bala 
limestone of North Wales, and that of the Chair of Kildare in Ireland; 
it also ranges into Llandovery strata. Zrinucleus concentricus, fig. 5, 
‘‘has a very extensive Lower Silurian range both in Europe and 
America.” Sil., 4th ed., p. 204. Jnchas laxatus, fig. 7, a perfect 
example of which is given in the above edition of Siluria, p. 204; 
Fossils (46, fig. 5), frequent in North Wales, is not uncommon in Cara- 
doc or Bala limestone of the Chair of Kildare; this species also ranges 
into the Llandovery rocks. Calymene brevicapitata, fig. 8, is a variety 
of the well-known Dudley fossil occurring in Lower Silurian strata of 
this age in Tyrone. This species, under the name of C. senaria, is 
included in the list of Caradoc fossils of North Wales as occurring at 
several localities in that district. Mus. G. 8., vol. iii, p. 2638. Homa- 
lonotus bisulcatus, fig. 9, 1s plentiful in the Caradoc sandstone of Shrop- 
shire. Spherexochus mirus, fig. 10, a very common fossil at the Chair 
of Kildare, is found perfect in the Wenlock limestone near Dudley ; 
and Phacops Brongniartt, confined to Caradoc strata, is found in North 
Wales, and occurs in profusion, often in a perfect state, in the slaty 
rocks of Tyrone, Waterford, and Wexford. 
FossI“ts oF THE LLANDOVERY Rocks. 
The Llandovery formation, described asa distinct group of strata by 
Sir R. I. Murchison, is named from the district in South Wales to the 
north and west of Llandeilo, particularly near Llandovery, where the 
passage from the underlying Caradoc rocks into the lowest member of 
