STOMACH OF PENTACRINITE. 439 
element, and, together with the column and 
arms, would yield to the direction of the current. 
Stomach. 
The abdominal cavity, or stomach, of the Pen- 
tacrinite, (PI. 51. Fig. 2.), is rarely preserved in 
a fossil state ; it formed a funnel-shaped pouch, 
of considerable size, composed of a contractile 
membrane, covered externally with many hundred 
minute calcareous angular plates. At the apex of 
this funnel was a small aperture, forming the 
mouth, susceptible of elongation into a proboscis 
for taking in food.* The place of this organ is in 
the centre of the body, surrounded by the arms. 
the articulating surfaces and of the bone itself, varies so as to give 
more universal motion as they advance towards the small extre- 
mity of the arm. See PI. 53, Fig. 14. a. b. 
In all this delicate mechanism which pervades every individual 
side arm, we see provision for the double purpose of attaching 
itself to extraneous bodies, and apprehending its prey. Five 
of these arms are set off from each of the largest joints of the 
vertebral column. At PI. 53. Fig. 7. a. we see the bases, or first 
joints of these side arms articulating with the larger vertebrae, 
and inclined alternately to the right and left, for the purpose of 
occupying their position most advantageously for motion, without 
interfering with each other, or with the flexure of the vertebral 
column. 
In the recent Pentacrinus Caput Medusae (PI. 52, Fig. 1.) 
the side arms (D.) are dispersed at distant intervals along the 
column. 
* This unique specimen forms part of the splendid collection of 
James Johnson, Esq. of Bristol. 
