284 Messrs. P. H. Carpenter and E-. Etlieridge, Jim., 



third brachials vary considerably in size. Neither of these 

 is an axillary ; but their terminal faces are almost transverse 

 to their longer axes, and seem to have been syzygial rather 

 than articular. No traces either of vertical or transverse 

 ridges are visible. 



In none of the specimens is there any indication of an anal 

 aperture. 



The interior of the calyx between the radials is occupied by 

 matrix ; but there are no signs of its having been roofed over 

 by a closed dome or vault of any kind. Had such a structure 

 existed within the circle of radial plates, it would assuredly 

 have been preserved in the original of f[^. 2, together with 

 the ring of first brachials. It is possible, however, as we 

 shall point out later on, that the mouth was surrounded by a 

 circle of oral plates, disconnected from the calyx like those of 

 the recent Rliizocrinus and Ilyocrinus. 



The column is short, and when tolerably entire has a ver- 

 miform appearance (PL XV. figs. 2, a, 6, & 7, a). It is 

 composed of small, low, rounded joints fitting closely toge- 

 ther. Each segment is biconcave, with a thickened margin, 

 and the centre a little raised around the small circular canal, 

 where the surface is also minutely frosted or granulated 

 (PI. XV. fig. 5). 



The surface of the plates is minutely pitted. 



The three specimens we have now described are from one 

 locality, together with another in a much broken condition, 

 and several fragments of other individuals. None similar 

 have been met with elsewhere. 



Other localities, on the contrary, have yielded a very large 

 number of small specimens, the general appearance of which 

 is so like that of the preceding examples that we have been 

 led to regard them as the younger stages of the same, or of a 

 closely allied species. They are all characterized by the 

 presence of an oral pyramid, the relative size of which is 

 greater the smaller the specimen. The various figures on 

 PI. XVI. and figs. 7, «, h of PL XV. represent a number of 

 these specimens of various sizes and at various stages of 

 development. Great as is the contrast between the originals of 

 figs. 1 and 2 (PL XVI.) and those of the corresponding figures 

 on PL XV., there are so many intermediate stages which pass 

 gradually into one another that we are unable to regard the 

 series as comprising more than one species. 



We may commence the study of this interesting develop- 

 mental series with the smallest and least advanced forms. 



such as are shown in figs. 1-3 (PL XVI.). The youngest 



