118 POTERIOCRINID^ PENTACBINUS. 



in all of the genus, are composed of a single series of wedge-shaped pieces, the thickest 

 ends of which alternately occupy a lateral position ; to the thickest ends of each of these 

 ray -joints a jointed tentaculum of extreme fineness is attached. 



The column is long and slender, the joints of which it is composed being thin and 

 generally uniform in size, except those near the body, where the new joints are thinner 

 than those below the first series of auxiliarj^ side arms. 



The claspers, like the column, are long and slender, they occur at wider intervals 

 and are longer than those of the typical species ; they are circular and composed of 

 thin joints, and emanate from the re-entering angles of the column. 



With this species of Pentacrinus, the Ophiura Egertoni was frequently associated, 

 for we find their remains occupying the same strata, and so intermingled that it is 

 probable the same physical catastrophe which prostrated the graceful lily-stars over- 

 whelmed the Ophiura in a common destruction. 



The specimens from which our figures are drawn were selected from among a group 

 of forty bodies of these animals, together with two Asterise, and numerous portions of 

 columns all embedded in one slab of stone eighteen inches in length by twelve inches 

 in width. This highly interesting group of crinoids was obtained at Bridport by 

 that indefatigable collector the late Mr. James Johnson, of Clifton, Hotwells, at whose 

 death, when his valuable collection was sold, and the treasures which it had taken a 

 long life to accumulate were dispersed throughout the civilized world, it became tlie 

 property of the British Museum, the most appropriate depository for such a splendid 

 relic of an ancient period in the Earth's history. 



We have dedicated this Pentacrinus to Mr. Job.nson as an acknowledgement of his 

 perseverance in collecting palceontological specimens, and of his liberality in throwing 

 open his museum to the scientific enquirer; and now that his labours have ceased, we 

 hope it will remain as a tribute to the momory of one of the most successful collectors 

 of fossils of our own times. 



The P. Johnsonii, though sufficiently abundant in some few localities of limited area 

 does not appear to have been very widely diffused, nor does its occurrence among the 

 fauna of a former period denote a prolonged geological existence. The slab of stone 

 containing so many individuals, and now in the British Museum, to which we before 

 adverted, contains by far the most perfect specimens hitherto discovered. Another 

 valuable group, but less perfect is in the Museum of the Bristol Institution. These, 

 with three or four other specimens of this Peniavrimis are all that have yet been 

 discovered and go far, to prove that the purpose for which it was introduced on our 

 planet was but of brief duration. 



