DESCRIPTIONS OF Till: S|'K< I Ms. Il'.i 



Remarks. This family was established by d'Orbigny 3 in L852 as one of tlio twelve 

 into which he divided the Crinoidea, and it is practically coextensive with the 

 '• family" Blastoidea of Say. According to d'Orbigny, it included armless Crinoids 

 which have the " calice ovalaire, solide, pourvu de cinq ambulacres reunis superieure- 

 ment ; chacuo strir en travels, pourvu d'un sillon au milieu et d'un pore a son 

 sommet." 



This definition would apply equally well to almost every one of the regular 

 Blastoids, except as regards the pore at the summit of each ambulacrum. The 

 extended form of it which was given by Dujardin and IIupc - commences with the 

 remarkable statement that " Ies Blastoides, ou Pentremitides, sont depourvus d'ap- 

 pareil digestif." For they believed the mouth to be only an "hiatus," and regarded 

 the anus as an ovarian opening. The remainder of their definition, which is too long 

 to quote, was based essentially upon Roemer's monograph, and, like him, they 

 only included in the " family " the three genera Pentremites, Elceacrinus, and 

 ( 'odaster. 



S. A. Miller has limited the family Pentremitidse, though without defining it in 

 any way, to the genera Pentremites and Granatocrinus. But we have been obliged 

 to remove the latter genus into a family of its own, as the presence of an hydrospire- 

 plate and the actual perforation of the deltoids by the spiracles distinguish it verj 

 sharply both from Pentremites and from Pentremitidea. 



The leading character of this family, as restricted by us, is the fact that the lancet- 

 plate does not fill the radial sinus, but leaves a passage on each side, which is bridged 

 over by the side plates. These form a roof to the hydrospire-canal, and also enter 

 into the distal border of the spiracle, as seen in Pentremites (PL I. fig. 6; PI. XVI. 

 fig. 21), Pentremitidea (PL IV. fig. 14 ; PL V. figs. 3, 19), and in Mesoblastus (PL VI. 

 figs. 8, 13). 



There is nothing of this kind in Orophoerinus, although the side plates may project 

 beyond the edge of the lancet-plate (PL XL fig. 8); while the hydrospires of Oryp- 

 tosehisma (PL V. fi^. 24), or of Phcenoschisma Archietei and P. caryophyllatum 

 (PL XIV. figs. 2-7) are altogether different from those of the Pentremitidse, 

 although the side plates project beyond the lancet-plate as in this family. 



Of the three genera which we refer to it, Pi nf remit idea occupies a curiously inter- 

 mediate position. For it has narrow ambulacra like Mesoblastus, but lacks the 

 hydrospire-plate of this genus, and in this respect it resembles Pentremites. In the 

 typical forms of the latter genus, and also in those of Pentremitidea, no division of 

 the five spiracular openings can be made out (PL I. figs. 4, 10; PL V. figs. 2, 4). 

 though it is sometimes rather marked (PL I. figs. 5, G, 11 ; PL IV. fig. 14) ; while it is 



1 'Cours elemeutairc de Palrnntologie et de Geologie stratigraphique,' Paris, 1852, t. ii. fasc. 1, p. 139. 



2 ' Hist. Nat. des Zoophytes Echinodermes,' 1862, pp. 56, 85. 



