on British Palceozoic Crinoids. 289 



The entire absence of orals from the three largest specimens 

 does not necessarily prove that they were not present during 

 life. We imagine that in the subsequent stages to those 

 represented in fig. 7 on PI. XV. and figs. 8-10 on PI. XVI., 

 the orals were relatively carried inwards, away from the radials, 

 and separated from them by perisome (just as they are in the 

 Pentacrinoid larva of Comatula) when the arms began to 

 appear above the radials. Whether the orals ever separated 

 so as to open the mouth to the exterior, and whether the ring 

 of perisome forming the ventral disk between them and the 

 radials was naked, as in Rhizocrinus j or plated, as in Hyo- 

 a-inus, must of course remain undecided. The absence of 

 any distinct anal system in the calyx of the large specimens 

 indicates that the anus was situated in a ventral disk, which, 

 if plated at all, can only have been but lightly so, as in the 

 Ichthyocrinidffi. It is true we have no proof that there were 

 any orals at all in the older specimens ; but, judging from the 

 relative sizes and development of the largest examples with 

 oral plates, and the smallest without, we think it scarcely 

 likely that they were entirely unrepresented in the adult. It 

 is obvious that, if they were united to the radials by perisome, 

 whether plated or bare, they would be readily lost under con- 

 ditions that would have had no destructive effect on younger 

 specimens, in which there was a closer union between the two 

 rings of plates. 



Lastly, we may say a few words about the ornament and 

 size of the specimens. In the larger individuals, although 

 visible, the pitted structure is not so decidedly apparent as in 

 many of the smaller and younger ones. For instance take 

 figs. 3 a and 10 a (PI. XVI.), as compared with figs, la, 2 a', 

 and 2h (PI. XV.). In the former it absolutely amounts to 

 ornamentation. 



The diameter of the full-grown calyx varies from about 

 3 millims. to 5 millims. 



3. On the Relations of the Species. 



Three or four years ago, when our acquaintance with Alla- 

 gecrinus was in a much less advanced state than at present, 

 specimens were forwarded to Prof. L. G. de Koninck of 

 Liege, for his opinion as to their identity. He very kindlv 

 referred one of the present writers to the description and 

 figure of the Poteriocrinus isacobus, T. and T. Austin *, as 

 coming nearest in general appearance to the specimens in 

 question. The identity of our little Scotch fossils with this 



* MoQ. Recent and Foss. Criuoidea, p. 74, t. 8. f . 4, a & b. 



