DESCRIPTIVE REMARKS. lxix 
of limestone, especially that of the Lower Limestone, generally ex- 
hibit their beautiful lace work structures in the greatest beauty and 
profusion. There is perhaps no spot where they may be better 
studied than on the promontory of Hook Head, in the county of Wex- 
ford, where the beds of limestone are almost horizontal, and large 
surfaces exposed, which are covered witha variety of Corals, Crinoids, 
Polyzoa, and Brachiopoda. 
The most frequent in the Lower Limestone and Carboniferous 
slate is Henestella antiqua, Pl. xxxvii., fig. 1, a, b. This species first 
appears in the Devonian. /. membranacea, fig. 2, a, b, is a funnel- 
shaped form with regularly arranged fenestrules, which, with others, 
are in such profusion in some limestone localities in Ireland as to give 
from their convolutions quite a character to the rock, which has in 
consequence been termed ‘‘ Fenestella”’ limestone. Polypora fastuosa, 
fig. 3, a, 6, is a species having numerous pores; and Retepora undata, 
fig. 4, a, 6, a form closely related to that of existing species,* Certopora 
rhombifera, fig. 5, a, b, a small branching Polyzoan of great beauty 
commencing in the Upper Devonian, is a common fossil in the Lower 
Limestone shale of Ireland. 
The Bracuropopsa are the most frequent and characteristic of all 
tho Mollusca in the Carboniferous Rocks; the accurate delineation 
and description of the numerous species, with their varieties, by 
Thomas Davidson, Esq., F. R. 8., in the Volumes of the Paleonto- 
graphical Society, lightens the labour of the Paleontologist in their 
identification. Of this class of fossil Bivalve shells more than 150 
species are enumerated. 
Of recent species, according to Woodward,} only seventy species 
were then known, whilst more than 1,000 extinct species had been 
described. For description of the parts of a Brachiopod shell see 
Descriptive Remarks, p. xxxvil., fig. 1, A, B, C. Zingula, Discina, 
Crania, Terebratula, and Rhynchonella, are genera which have lived 
on to the present day. 
Lingula squamiformis, Plate xxxvii., fig. 6, a, 6, ec, belongs to a 
genus the most persistent of all fossils, commencing in the lowest 
fossiliferous rocks, it has continued through all the strata to the 
present day. ‘This species commences in the Upper Devonian and 
continues to the Coal Measures. 
Discina (formerly Orbicula) nitida, fig. 7, a, 6, is an orbicular 
shell common in the Clay Ironstone of Coalbrook Dale. It commences 
(according to Mr. Etheridge) in the Upper Devonian continuing on to 
the Coal Measures. 
Crania quadrata, fig. 8, a, b,c, is a less common fossil; it is, how- 
ever, one of the genera which continues to the present day, and has 
been found in English, Scottish, and Irish strata. Zerebratula has- 
tata, fig. 9, a, 6, is a common fossil in the limestone, of which 7’. 
* See Descriptive Remarks, ante p. Xxx, fig. 8. 
+ Manual of Mollusea, 1854. 
i 2 
