m IIADIATA. CnmOlDM. Pentacrinus. 
foreign bodies ; from a depression in the centre of this plate arises the filiform 
column, slightly incrassated towards the summit, and capable of bending or 
twisting, composed of about twenty-four joints ; the external form and inter- 
nal structure of the column not ascertained. Axillary side arms in a single 
row around the last joint of the column, corresponding with each of the costals, 
re volute, composed of about ten joints, the terminal one hooked. Plates of the 
pelvis too obscure to be determined. The first costals are thick, wedge-shaped, 
broadest upwards, the distal extremity emarginate, and supporting a second 
costal of a narrow subconical form, truncated and emarginate where it joins 
the scapula. The summit of the scapula is angular, having a sloping face on 
each side, for the attachment of the first arm joints. The arms are ten in 
number, and being supported on scapulae greatly narrower than the first cos- 
tals, are rather remote at their base. The arms consist of about twenty-four 
solid joints, tapering towards the extremity, simple in youth, but with age 
and size dividing and subdividing ; along the side a row of dark spots ; each 
arm supports on each side, in an alternate order, a row of annulated cylin- 
drical, flexible, fleshy processes, covered with capitate filaments. The arms 
in these respects resemble those of the Comaiula, in which I have observed a 
similar row of brown tubercles with a granular surface, a fleshy production 
on the ventral margin of the arm, broadest at the middle, supporting cylin- 
drical processes, fringed with smaller filaments, ending in an expanded 
sucker-like extremity. Within the costals, the body is subglobular, in the 
centre of which is the mouth, formed by five petal-like valves, within which 
are several soft tentacula ; without the valves is an opening with a tubular 
extensile margin, supposed to be the vent. In the early stages of its growth 
neither column nor arms are visible, the body appearing like a little club, fixed 
by an expanded basis, and giving exit, at its apex, to a few pellucid tentacula. 
The existence of the second aperture in the body of the genus Comatula, which 
Mr Thompson, in the interesting paper from which we have extracted the de- 
scription of this species, supposes not to have been previously observed, was 
known to Mr Adams thirty years ago, and described by him in the Linnean 
Transactions published in 1800. In the Annals of Philosophy for Nov. 1806, 
Mr Gray likewise announced the existence of this second ^aperture, without 
being aware of its previous detection. If|future observations, on better pre- 
served specimens, shall confirm the results of Mr Gray’s examination of the 
recent Pentaerinus caput Medusas^ and demonstrate that it has but one open- 
ing to its alimentary canal, it will be necessary to constitute this species, dis- 
covered by Mr Thompson, into a new genus, which may be termed Hiber- 
NULA (the forerunner we hope of many important additions to our Fauna, 
when the shores of Ireland shall have been more extensively explored), and 
by characterising the family Comatulada:, as possessing, besides numerous 
other common properties, an alimentary canal with two openings, it will be 
naturally divided into two sections, the first containing VdQ fixed Hihernula^ 
the second the free Comatula. 
EXTINCT SPECIES. 
1 . P. MiZ/m.— -Auxiliary side-arms round, in single series ; column smooth ; 
columnar joints generally alternately smaller and larger.— -P. Caput-medusae, 
Mill. Crin. 56. — In Lias. 
2. P. hasalitiformis Auxiliary side-arms round, in single series ; column 
smooth ; columnar joints generally of more uniform thickness. — Mill. Crin. 
G2.—Lias. 
3. P. tuberculatus Auxiliary side-arms round, in single series; column 
tuberculated. — Mill. Crin. 64. — Lias. 
4. P. Auxiliary side-arms round, in a double series. Mill. 
Crin. 59.— In Lias. 
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