Tex DESCRIPTIVE REMARKS. 
sacculus., fig. 10, a, b, ce, may be merely a variety, as suggested by 
Mr. Davidson. Lynchonella pleurodon, fig. 11, a, 6, is a very abundant 
shell, especially in Lower Limestone; and R. pugnus, fig. 12, a larger 
form not so frequent, but nevertheless a characteristic shell. Spird- 
fera striata, Pl. xxxvii., fig. 1, a, 6, belongs to a genus which includes 
many Carboniferous species. This species is remarkably prevalent 
through all the divisions of Carboniferous strata from the lowest to: 
the highest. Spurifera cuspidata, fig. 2, is another form not so fre- 
quent as the last named species, but still abundant in England and 
Ireland. Anthyris ambigua, fig. 3, a, b, c, an intermediate form be- 
tween Zerebratula and Spirifer, differs from the former in having an 
internal spiral arrangement like the latter. Orthis resupinata, fig. 4, 
a, 6, is one of the most frequent fossils in the Carboniferous Limestone. 
Productus semireticulatus, fig. 5, a, b, c, also occurs in profusion. The 
Productide are exclusively Paleozoic and attained their maximum 
during the Carboniferous Limestone period; entire beds are made up: 
of the large shell Productus giganteus. Chonetes papilionacea, fig. 6, a, b, 
belongs to a genus which also attained its maximum during the Car- 
boniferous period. Streptorhynchus crenistria, fig. 7, a, b, is frequent 
in the Lower Limestone. 
The Concuirera, or Bivalve shells of the Carboniferous Rocks, in- 
clude a considerable number of genera and species. Of Aviculopecten, 
which contain a large variety of forms, we have selected A. papyraceus, 
Pl. xxxix., fig. 1, a shell found associated with Gonzatites in the black 
shales (marine deposits) of the Coal Measures, both in England and 
Ireland. A. granosus, fig. 2, common in the Limestone, and 4. 
Sowerbiz, also abundant in the Limestone, especially of Ireland, and 
showing colour markings. An allied shell Posidonomya Bechert, fig. 4, 
also a marine species, is a fossil which in Ireland occurs in abundance, 
and marks a particular horizon between the Upper Carboniferous and 
the Lower Coal Measures; it is also frequent in the Culm of Deyvon- 
shire, and thus a clue is obtained as to the true position the beds in 
which it occurs occupies in the Carboniferous series. 2. membranacea, 
fig. 5, is a smaller and transverse form common in the Lower Coal 
Measure shales in the south and central parts of Ireland. JIodiola 
Macadam, fig. 6, is especially characteristic of the Lower Limestone 
shale in Ireland. Pleurorhynchus Hibernicus, fig. 7, a, 6, is abundant, 
and attains a large size in the Carboniferous Limestone of Ireland. 
Anthracosia centralis, fig. 8, is a unio-like shell, indicating a brackish 
water deposit, frequent in the Coal shale of the Midland counties. 
Myacites Omaliana, fig. 9, is not unfrequent in the Carboniferous 
Limestone of Ireland. Cardiomorpha oblonga is another characteristic 
species in the Carb. Limestone of Ireland. Curtonotus elegans, fig. 11 
a, 6, are smaller bivalves, frequent in Lower Carboniferous strata, 
‘¢ Coomhola Grit” of the South of Ireland. 
The GastERoPopa are also represented by a considerable number of 
forms in the Carboniferous Limestone; WVatica plicistria, fig. 1, is a 
frequent species; Loxonema impendens, fig. 2, is a species common in 
