Stomach.
The abdominal cavity, or stomach, of the Pentacrinite, (Pl. 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.[1] The place of this organ is in the centre of the body, surrounded by the arms.
Body, Arms, and Fingers.
The body of the Pentacrinite, between the summit of the column and the base of the arms, is small, and composed of the pelvis, and the costal, and scapular plates, (See Pl. 51. Pl. 52. Fig. 1. 3. and Pl. 53. Fig. 2. 6. E. F. H.) The arms and fingers are long and spreading, and have numerous joints, or tentacula; each joint is armed at its margin with a small tubercle, or hook, (Pl. 53. Fig. l7.,) the form of which varies in every joint, to act as an organ of prehension; these, arms and fingers, when expanded, must have formed a net of greater capacity than that of the Encrinites.[2]
We have seen that Parkinson calculates the number of bones in the Lily Encrinite to exceed twenty-six thousand.
- ↑ This unique specimen forms part of the splendid collection of James Johnson, Esq. of Bristol.
- ↑ The place of the Pentacrinites in the family Echinoderms, would lead us to expect to find minute pores on the internal surface of the fingers, analogous to those of the more obvious ambulacra of Echini; they were probably observed by Guettard, who speaks of orifices at the terminating points of the fingers and tentacula.
Lamarck also, describing his generic character of Encrinus, says: "The branches of the Umbel are furnished with Polypes, or suckers, disposed in rows."
