W. A. Parks — Lepadocystis clintonensis. 405 



zon, the Clinton, is worthy of note. This formation is pos- 

 sessed of a very meagre Echinoderm fauna, the exposures in 

 Ontario having yielded only a few fragmentary Crinoids. The 

 present example lay for a long time in our collection as an uni- 

 dentifiable specimen. Recently, however, an attempt to clean 

 it was made with unexpectedly satisfactory results. By sawing 

 the specimen out and treating it with caustic potash the organ- 

 ism was entirely freed from the matrix, so that it now shows 

 the chief anatomical peculiarities in an excellent manner. 



Adopting the method of numbering the plates proposed by 

 Forbes,* we have, in the lower circlet, four plates, of which 1 

 and 2 are regularly pentagonal. Plate 4 is irregularly penta- 

 gonal, and 3 is hexagonal with its upper edge curved inwards. 

 Of the second circlet, plates 5 and 6 are irregularly hexagonal: 



Fig. 2. 



ft 



CO d> & CO 



Fi«. 2. Dissection of cup. 



7 is also hexagonal, but it has an heptagonal appearance owing 

 to the encroachment of the anal orifice on its upper, right- 

 hand angle. Plate 8 is smaller than 7 and is likewise deeply 

 cut by the anus on its upper left-hand corner ; its lower side 

 is curved to fit into plate 3. Plate 9 is irregularly hexagonal. 

 Of the third circlet, plates 10, 11 and 12 are hexagonal, but 12 

 is larger and more irregular than the other two. Plate 13 is 

 narrower and reaches farther up the cup than any other plate 

 of the ring : it is five-sided or six-sided if the deep anal exca- 

 vation on its lower right-hand angle is included. Plate 14 is 

 large and hexagonal, with the anal notch in the lower left-hand 

 corner. The five plates of the fourth circlet (16, 17, 18, 19, 

 15) are pentagonal with the upper margin deeply notched for 

 the ambulacral furrows. The plates of the fifth circlet (21, 22, 

 23, 24, 20) are small and almost indistinguishable in the speci- 

 men. 



All the plates of the cup are ornamented with polygonal 

 ridges, separated by shallow depressions. On the first two 



* Memoirs of the Geol. Survey of Great Britain, vol. ii, pt. ii, p. 488. 



