120 POTEEIOCRINID^ PENTACRINUS. 



This species in its strong rays and broad tentacula presents a complete contrast to 

 the more delicately formed P. Johnsonii, in which all the parts are extremely neat and 

 slender, while every portion of the tuberculatus is indicative of strength. From this 

 it may be inferred that the food of the one was minute and unresisting, while that which 

 sustained the other was capable of exercising some degree of activity in eluding the 

 tenacious grasp of its destroyer. 



The jointed tentacula fit into curved notches or depressions in the sides of the ray 

 joints. 



It is somewhat remarkable that nearly all the columns of this species are found in a 

 curved position, indicating that during life they must have possessed a considerable 

 degree of muscularity. The joints being thinner, though of greater diameter than those 

 of the P. Caput Medusee, will partly account for this, for in consequence of their tenuity 

 the intervening muscles must have been more numerous, and consequently on the death 

 of the animal the irregular shrinking of the fibres may have caused the peculiarity 

 alluded to, aided perhaps by the rupture on one side of the muscular tunic which 

 enveloped the external surface of the column. By the gradual contraction of this part 

 it would at length become rent and thereby allow the integument on the opposite side 

 to contract more freely, so that it would have drawn the column by degrees into a curve, 

 while the ruptured portion would offer no resistance to its assuming the form in which 

 we now constantly find it. 



4. Species. Pentacrinus Millerii. 

 Plate 16, Figure 1 «, to ] f. 



Description.— Body small, forming a pentagon; rays long and bifurcating ; colunni 

 pentagonal and slender, and furnished with circular claspers. 



Synonymes and References. 



Pentacrinites scalaris. — Goldf. t. 52, /. 3, /. 60, f. 1 0. 



— Park. Org. Rem. vol. 2, I'late 13. 

 —Mill. Nat. Hist. Crin. page 61. 

 — Morris, Cat. Brit. Fossils, p. 56. 

 — Knorr, suppl. 7, g. n, 205, Jigure 4 — 8. 



