112 POTERTOCRINID^ PENTACRINUS. 



the boats, and the lower parts left attached to the rocky bed of the sea, thus in a great 

 measure proving they were fixed by an indurated base of calcareous matter. 



It is extremely doubtful whether the P. Caput Medusae has ever been found in a 

 fossil state, the specimens of columns found in the lias near Bristol, Ke3'nsham, 

 Hengrove, &c., and generally referred to this species may probably belong to some 

 other Pentacrinus. If it does occur in a fossil state we should expect to find it in 

 the newer tertiary rocks, but none of the specimens hitherto obtained from any of the 

 tertiary beds can with safety be referred to this species. 



The dorso-central plate appears to be formed of an enlarged columnar joint. This 

 may possibly be divided into five wedge shaped pieces as stated by Miller, but if so 

 the divisions are not manifest in any of the specimens we have examined. 



In the five sinuosities or retiring angles of the dorso-central plate, the five perisomic 

 lateral pieces are placed. These pieces are truncated at their upper edges, where they 

 partly slope inwards towards the columnar canal. They have two slight ridges with 

 perforations for the articulation of the primary rays. These lateral pieces are exteriorly 

 lunated, and their lower ends extend downwards to a level with the lower edge of the 

 dorso-central plate, but they do not overlap the column as in the preceding genus, 

 (E,vt)ricriiiiis.J 



On the five lateral pieces the same number of primary or main rays of two joints each 

 articulate,but the number of joints is not uniformly constant. The firstjoints of these rays 

 were considered by Miller as the second costals, but his own description of them is almost 

 conclusive evidence of his error respecting them. It is as follows, — " The figure of these 

 joints is that of a horse-shoe, having in the interior an excavated truncated termination. 

 The exterior surface is semicircular, and their lateral edges do not adhere to each other, 

 but are united hy the integinnent coreriug the abdominal caritg." This description is quite 

 correct in one sense, but not in another, for the fact of the pieces not adhering to each 

 other is strong evidence that he is wrong, for in all the crinoids we have examined the 

 pieces composing the body invariably adhere to each other laterally, and it is difficult to 

 concieve why Miller should have deviated from a rule, which may be considered as 

 universal. Parkinson, who, in this respect is equally correct in his description of this 

 species as he is in describing the E. Briareus, considers these pieces as portions of the 

 rays. The second joints of the primary rays, (the scapula of Miller) have each a central 

 ridge extending from the exterior edge of the joint to the interior, thus forming two 

 sloping surfaces, like the slanting roof of a house, for the adhesion of the secondary rays 

 which here branch off into a pair. On each of these sloping sides is a perforated ridge, 

 which runs in an oblique direction from the inner edge of the joint towards its outer 

 circumference where it unites with the corresponding ridge on the opposite slope. These 



