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ADDENDA TO THE GENUS PENTACRINITES. 
Mr. James Sowersy, of Lambeth, has kindly presented me with fragments 
of the column of a Pentacrinite, found by him in the London clay, about 6 or 
8 years ago, at White Conduit-House, Islington; adding that they also, 
though rarely, occur at Richmond, and have been-met with in digging a well 
at Kensington ; but he further remarks that they are generally so much im- 
pregnated with pyritical matter that they soon decompose and fall to pieces. 
These columns much resembles in size and shape those of Pentacrinites 
basaltiformis, but have the angles more rounded. From their exhibiting no 
marks of muscular corrugation at their exterior surface, and the joints being 
of uniform thickness, I apprehend the fragments before me to be full grown 
columnar portions. I wave distinguishing it as a species, not having the means 
of furnishing a specific character; yet, should it prove such, I should propose 
for it the name Pentacrinites subbasaltiformis. 
I apprehend this is the same species which is mentioned in Dr. 
Woopwarp’s catalogue of the additional English native fossils, vol. 11. p. 51. 
x. d. 58. to 60. as having been found in the same stratum. 
CONCLUSION. « 
The interesting fact observed in the Crinoidea of the preservation of the 
investing muscular membrane, and the retention of the form produced by its 
various contractions in a fossil state, which has been proved by the detailed 
description of its traces in various specimens, created a wish to discover 
whether similar traces might not likewise exist in the fossil Echini and 
Cidares ; since in these animals the plates inclosing the viscera are covered by 
an investing muscular membrane considerably analogous to that of the 
Crinoidea, and employed in communicating motion to the spines. 
Considering the figure of the Echini and Cidares attentively, I discovered 
that by reversing the terms upper and lower surface (as usually applied) 
and by placing the animal with its mouth upwards, a greater analogy than I 
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