296 CATALOGUE OF THE BLASTOIDEA. 



and Yandell. One of the two at the origin of the odd ambulacrum is probably the 

 anal spiracle, as we have endeavoured to point out on pp. 14, 15. 



We cannot venture to offer any explanation of these striking peculiarities of 

 Eleutherocrinus, but will pass on to consider its resemblance to the Carboniferous 

 genus Astrocrinus, which is closer than would appear at first sight. Astrocrinus has 

 four long and narrow ambulacra, which cross one another almost at right angles, and 

 a short odd one as well (PL XIX. fig. 1). There is an azygos radial which is not 

 incised at all, but merely notched to receive the distal end of the odd ambulacrum 

 (PI. XX. figs. 14, 19, 20), and it rests upon the upper edges of two long basals, as in 

 Eleutherocrinus (PI. XIX. figs. 1, 15). Sometimes, as shown in the first of these 

 two figures, the small basal, x, seems to have fallen away from its dorsocentral 

 position ; but in other cases it cannot be distinguished in the granular lower surface 

 of the calyx (PL XX. figs. 8, 10, 13). 



These two genera, Astrocrinus and Eleutherocrinus, are thus united by several very 

 definite characters, and may be associated together in one family, for which it is only 

 right to use the name Astrocrinidse, T. & T. Austin, 1843, though it was never 

 formally denned. With these two genera we must associate, at any rate for the 

 present, the very singular internal cast which was described by Haughton 1 in 1859 

 as Pentephyllum Adarense (PL XVI. figs. 14-16). It is unstalked, like Eleuthero- 

 crinus and Astrocrinus, so that the physiological condition which is presented by 

 Marsupites and Uintacrinus among the Neocrinoids, to say nothing of the Comatulse, 

 was also reached by some half dozen members of the older group of Blastoids. 

 For the opportunity of examining this fossil we are indebted to our friend Prof. W. 

 J. Sollas, F.G.S., of Trinity College, Dublin. It is not altogether symmetrical in 

 outline, but its base is very regularly pentagonal (PL XVI. fig. 16), a character 

 which at once distinguishes it from Astrocrinus and Eleutherocrinus (Fig. VIII, A). 

 Its deltoid plates are large like those of Astrocrinus, and the radio-deltoid sutures have 

 exactly the same relations as in Codaster (PL XII. figs. 1, 4), descending the sloping 

 sides of the radial sinuses and meeting the ambulacra nearly at right angles (PL XVI. 

 figs. 14, 15). The interambulacral angles are not equal, however, as they are in the 

 regular Blastoids, but they have the same want of symmetry as Eleutherocrinus, four 

 of them taking up a little more than 180° of the summit. There is a fracture in the 

 summit at the origin of the odd ambulacrum, but enough remains to show that this 

 was linear like its fellows (PL XVI. fig. 14), and not largely modified as in Astro- 

 crinus and Eleutherocrinus (PL XIX. figs. 1, 6). 



Pentephyllum then clearly belongs to the Order Irregulares, and until we know 

 more about it, we think that it had better be placed in the family Astrocrinidse, 

 which will have the same definition as the Order. 



1 " On a new Carboniferous Echinoderm, from the County of Limericli." Journ. Gool. Soe. Dublin, 1859, 

 toI. viii. p. 183, pi xxix. 



