212 SILURIA. [Chap. IX. j 
from Galway. Orthonota semisulcata, Sow., is recorded by that author from k 
the Ayrshire sandstone, and 0. rotundata, PI. XXIII. f. 5, from Galway; i 
where, too, a solitary species of Pleurorhynchus (PI. pristis, Salter) has been 
found. 
If the Lamellibranchiate Shells do not present any marked characters, it is ! 
otherwise with the Gasteropods, which are numerous and peculiar. Both tur- 
binate and elongate forms abound — such as angular species of Pleurotomaria and 
Murchisonia, the depressed form Raphistoma (so common in the Lower Silurian), [ 
Euomphalus, Trochus ?, Holopea, and Holopella. Macrocheilus, Acroculia, Pa- 
tella, and even Chiton are also found here. The last is particularly interesting, 1 
carrying back, as it does, a marked and common living genus to this Middle Si- 
luriantime. It is of so elongate a form that the term Helminthochiton was ap- 
plied to it by Mr. Salter, who described it so far back as 1846 in Sir R. Griffith's 
Synopsis of the Silurian Fossils of Ireland. Acroculia Haliotis, Sow., is rare in j 
the upper beds, in which only Euomphalus funatus, Sow., and Eu. sculptus, Sow., 
so abundant at Tortworth, are found. There are some undescribed species of 
Turbo — though some shells referred to this genus evidently do not belong to it, ; 
being with strong strise of growth, and raised ridges round the whorls. Such are ' 
Trochonema trochleata of M'Coy and T. tricincta, M'Coy, from Galway ; and 
such also may be the thin American shells called Cyclonema by Hall, and of j 
which C. ventricosa of that author is found at Tortworth. The little Turbo I 
tritorquatus, M'Coy, from Llandovery, and also from Galway, may belong to this I 
group ; there is but slight evidence, however, that any of the above-named spe- 
cies belong to the genera to which they have been assigned. 
The genus Trochus, so-called, contains two, if not three species. T. Moorei, j 
M'Coy, is probably a Pleurotomaria ; but the T. multitorquatus of that author, | 
which (or an allied species) appears to occur both in Ayrshire and Pembroke- 
shire, can scarcely be referred at present to any other genus. It is a most re- ! 
markable shell, with at least seven flat whorls. Pleurotomarise and Murchisoniae 
are common fossils. Murchisonia Prycese, Sow., and M. angulata, Sow., PI. X. J 
f. 11, 12, are found throughout the Lower Llandovery of Wales. The inhabi- | 
tants of these shells seem to have delighted to live upon the sandy and pebbly 1 
shoals which, now formed into conglomerate, are so frequent in the hills on the 
right bank of the Towy. Murchisonia simplex, M'Coy, is found in similar situa- 
tions, but in a less coarse matrix j it is chiefly a Lower Silurian species. M. 
cancellatula, M'Coy, is an Ayrshire fossil, and M. pulchra, M'Coy, a Galway 
species. A large angular shell, to which Mr. Salter applies the MS. name M. ; 
bicoronata, is very common at Haverfordwest and in other parts of Wales. 
Raphistoma lenticularis, PI. X. f. 10, is everywhere met with in the Llandovery 
rocks. Two or three species of Holopella (Turritella of my old work) are found 
in the same zone at Tortworth, and appear to be also the common species of the 
uppermost Ludlow rock — H. obsoleta, Sow., H. gregaria, Sow., &c. These have 
been found in Galway too by M'Coy, as well as H. plana, M'Coy. H. tenui- 
cincta of the same author is a Lower Llandovery form, while H. cancellata, 
Sow., our largest British species, often three inches long, is common to the 
Lower and Upper Llandovery, and abounds in still higher beds at the Bogmine 
near Shelve in Shropshire. An angular- whorled Loxonema is found at Marloes 
Bay ; and Macrocheilus fusiformis, Sow., the largest of the Gasteropods of the 
Llandovery rocks, is a rare fossil from Presteign. 
The Pteropods contribute a few species, of which Conularia Sowerbyi,Pl. XXV. 
f. 10, Ecculiomphalus Scoticus, M'Coy, and a fine species of Pterotheca are the I 
