ADDENDA TO THE GENUS PENTACRINITES. 



Mr. JAMES SOWERBY, of Lambeth, has kindly presented me with fragments 

 of the column of a Feiitacrinite, 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 

 basal tiformis, 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. 

 WOODWARD'S catalogue of the additional English native fossils, vol. n. 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 

 \arious 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 



