Chap. IX.] 
FOSSILS OF THE LLANDOVEEY ROCKS. 
213 
chief. The last, which much resembles Pt. transversa, Portl., of the Lower Si- 
lurian, occurs in the Upper Llandovery rock of Tortworth. 
Of Bellerophon, no less than eight species have been already observed, and 
there are probably many more. The great B. dilatatus, PL XXV. f. 6, is found both 
in Lower and Upper Silurian, as well as in this band. B. bilobatus, PI. VII. f. 9, 
so common in the Caradoc sandstone, and so characteristic of the Lower Silurian 
of France, Spain, arid Bohemia, ranges up into the Lower Llandovery in Ayr- 
shire, where B. subdecussatus, M'Coy, and at least two other unnamed species 
occur. Lastly, B. trilobatus, one of the uppermost Ludlow or Tilestone species, 
PI. XXXIV. f. 9, is found both at Tortworth and in Galway. 
A few Cephalopoda only have yet been described from these deposits, though 
they are not rare. Orthoceratites, of both smooth and annulated forms, are in- 
deed often met with. Orthoceras conicum, Sow., of the Sil. Syst. pi. 21. f. 21, 
is perhaps the most frequent in the upper beds. 0. Barrandii, Salter, of Ayr- 
shire, is one of the shortest forms known, and is figured in the Quart. Journ. 
Geol. Soc. vol. vii. pi. 9. f. 19. 0. tenuistriatum of Minister, a species with fine 
longitudinal striae, occurs at Haverfordwest and in Ayrshire ; and 0. bullatum, 
PI. XXIX. f. 1, and 0. angulatum, PI. XXVIII. f. 4, are quoted by M'Coy from 
Galway. Prof. M'Coy mentions five or six smooth species from the Galway beds, 
including 0. tenuicinctum of Portlock. As these species range from Lower to 
Upper Silurian, it is most important to note this fact in treating of a band which 
unites those two great divisions. 
The most remarkable of all these Cephalopods is Tretoceras bisiphonatum, 
figured in PI. XI. f. 5, from the Upper Llandovery rocks of Gorllwj^n, near Llan- 
dovery, South Wales. It looks like an Orthoceras with a double siphuncle ; but 
(as shown by Mr. Salter *) it has a deep lateral tube piercing the septa, as well 
as a siphuncle. This remarkable fossil should be sought for by collectors. Litu- 
ites cornu-arietis, Sow., a Caradoc species, ocurs in the lower division of these rocks 
at Llandovery ; Cyrtoceras (Orthoceras, Sil. Syst.) approximatum, PI. XL f. 4, 
at Eastnor Park ; and a fine large species, yet unnamed, of the latter genus has 
been obtained from the precipitous strata of Castell Craig Gwyddon, near Llan- 
dovery. Lastly, Phragmoceras (?) compressum, PI. XXXI. f. 4, a Wenlock fossil, 
has occurred, with many Lower Llandovery species, in the hard sandstones of 
Thrave, near Girvan, Ayrshire. 
Annelida are plentiful, both Tentaculites Anglicus, PI. I. f. 3, and Cornulites 
serpularius, PI. XVI. f. 3-10, being the common fossils in Tortworth and other 
districts. They are less frequent in the lower division. Tentaculites ornatus, 
PI. XVI. f. 11, is rare, but is found in Ayrshire. 
Of Trilobites few species are characteristic. If we except Phacops Weaveri, 
Salter f, a large species of IHsenus like II. Bowmanni, Salt., which is frequent in 
South Wales, and also occurs in Shropshire and Scotland, there are no forms 
known to be peculiar to this intermediate formation. Of these species it is re- 
markable that the Phacops Weaveri is found in beds of corresponding age at 
Point Gaspe, in the distant region of Canada. The species of Illaenus above 
quoted differs considerably from II. Bowmanni of the inferior rocks, which, never- 
theless, is found here with it. The last-named fossil, with Lichas laxatus, 
M'Coy, and probably Asaphus latifrons, Portlock, or its closely allied form, are 
three Lower Silurian species of Trilobites which range into these Llandovery 
rocks. The other Trilobites are well-known Upper Silurian types, viz. Phacops 
Stokesii, Edw., and P. caudatus, Brongn. (the former common, the latter rare), 
Quart. Journ. Geol. Soc. vol. xiv. p. 177. 
t Mem. Geol. Surv. Decade i. pi. 1. f. 16. 
