:U ECIIINODERMS OF THE LONDON CLAY. 



not tliickcn or swi'll out at the point of jnnction. Tlic live plates of the pelvis alternate 

 with five large, slightly convex, ascending primary radials, which bear the first arm-])lates 

 large also, but of only half the lu'ight. All the plates are smooth. The arms, &c., are 

 destroyed. The column is imcompressed, very equal iu its proportions, very smooth, with 

 slightly imdulating joints, whose sutures appear slightly curved externally, and whose 

 articular surfaces are roughly radiated. The perforation is very small. The whorls of 

 ramules are very distant ; their sockets arc large and deeply impressed. They are 

 slender, but strongly jointed. 



Ge?ius — Pentacrinus, Miller. 



Cup very shallow, constituted of a pelvis com[)ose(l of a single piece formed out of 

 five ancliylosed plates, alternating with five primary radials. Column more or less 

 distinctly pentagonal ; furnished with articulated ramules. Joints with stellated articular 

 surfaces. 



1. Pentacrinus subbasaltiformis. Plate IV, figs. 8, 'J, 10. 



Pent.\crinus suBBASAT.TiroBMts, Miller. Nnt. Hist, of Crinoidea, p. 110. 



— — Wetherell. Trans. Geol. Soc, London, 2d series, 



vol. V, pt. 1, p. 136, pi. viii, fig. 4. 



— — Austen. Monog. Rcc. and Fos. Crinoidea, p. 122, 



pi. xvi, fig. 2. 



— DiDACTYLUs, Aidde If Orbigny . Mem. Soc. G^ol. France, 2''' ser. vol. ii, 



pi. V, fig. 18? 



Miller, in his famous work upon Crinoidea, proposes the name of Pentucrinites 

 sivhhasaUiformin for the columns of a Crinoid, found by Mr. James Sowerby in the 

 London Clay at AVhite Conduit House, Islington, and mentions that similar colunnis occur 

 at Richmond and at Kensington. He remarks that " these columns nuich resemble 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 sui'facc, and the 

 joints being of uniform thickness, I apprehend the fragments before rae to be full grown 

 colunmar portions." It was figured by Mr. Wetherell in the illustrations to his paper 

 entitled " Observations on a Well dug at Hampstcad Heath," and since by Mr. Austin, 

 in his " Monograph of llecent and Fossil Crinoida^a." 



Numerous fragments of stems have been found. These vaiy from round to very obtusely 

 pentangular, and from five lined to five grooved along this length. The joints are of equal 

 dimensions, and are plane and (|uite smooth externally. The articular surfaces present 

 rounded crenated lobes. At intervals, ramules are given ofl" opposite, or very nearly oppo- 

 site, each other, disturbing the symmetry of the joints from which they spring. In the 

 example represented, Plate IV, fig. 8, the diameter of the joints is one fomlh of an inch, 

 and their altitude one tenth of an inch. 



