472 
CIRR1PEDA. 
Genus 2. —CREUSIA.— Leacli. 
Generic Character. —Body sitting, subglobular, inclosed in an 
operculated shell; having three or four pairs of tentacular arms. 
Shell sessile, fixed, orbicular, convexo-conical, consisting of 
four united unequal valves; operculum interior and bivalve. 
Creusia verruca. — The Warted Creusia. 
Plate XCII. fig. 7. 
White; slightly depressed, with interwoven obliquely striated 
valves ; the margin at the base irregularly serrated. One-fourth 
of an inch broad. Inhabits the British seas. 
** Opercula with four valves. 
Genus 3. — A C A S T A.— Leach. 
Generic Character. — Shell sessile, ovate, subconic, compress¬ 
ed, and consisting of six parts, two of the valves small, and four 
large, slightly united, having an orbicular plate concave inter¬ 
nally at the base. 
Acasta Montagui. — Montagu’s A casta. 
Plate XCII. fig. 8, 9. 
Valves erect, triangular, acute, with muricated ascending 
spines. Inhabits the British seas. 
Genus 4.—ADNA.— Leach. 
Generic Character. —Cup-shaped, sessile, shell composed of 
one part; aperture lozenge-shaped ; with four valves. 
Adna Anglica. —The English Adna. 
Plate XCII. fig. 28. 
Shell and base externally, and slightly ribbed; of a fine rose 
colour; operculum transversely striated. Inhabits the Devon¬ 
shire coast, attached to the Coryophyllia Anglica. 
Genus 5.—BALANUS.— Bruguiere. 
Generic Character. —Body sessile, inclosed in an operculated 
shell; branchiae numerous, placed in two rows, unequal, articu¬ 
lated, ciliated; each composed of two cirri, supported by a pe¬ 
duncle, and exsertile ; mouth with four transverse and dentated 
