THE ETDEOSPIEES ami sni; \('Li:s. 91 



the uppermost of the seven slits, at any rate are excavated in the substance of the 

 calyx-plates, as in Phcenoschisma (PI. XVII. figs. L5, 1(1). The two inner hydro- 

 spire-folds have thickened edges (PI. XV. lip. 10), and upon these, bridging over 



the gap into the visceral cavity, there re.-sts the under lancet-plate, itself with a 

 prominent rim. 



Owing to the small size of the deltoids nearly all the hydrospires are supported 

 by the radial limbs, as is well seen in the same figure (PI. XV. fig. L0). It also 

 shows that the visible hydrospires do not extend quite to the distal end of the sinus, 

 though the tubes perhaps pass into the substance of the radials as in Pentremites, 

 Triccelocrinus, and other genera (PI. II. fig. 81; PI. III. figs. 6, 8; PI. XVIII. 

 figs. 11, 13). Both in the English and in the Belgian varieties of 0. pentangularis, 

 but especially in the latter, the radial sinus is reduced to a relatively wide hydrospire- 

 cleft extending along the whole length of the ambulacrum. This is nowhere in 

 contact with the sides of the sinus (PI. XV. figs. 5, 8, 10 ; PI. XVI. fig. 8), so that 

 the slits open directly to the exterior through the hydrospire-cleft, the proximal 

 end of which is uot separated off as a spiracle any more than in 0. Orbignyanus 

 (PL XIV. fig. 1C). 



In the other English species, 0. vcrus, however, the under lancet-plate which 

 bears the ambulacrum, is in contact with the sides of the radial sinus for rather 

 more than the distal third of its length so that the hydrospire-cleft is considerably 

 shortened (PI. XV. figs. 3, 4) ; though at the same time it is continued as a canal 

 beneath the under lancet-plate. But its proximal end is nowhere bridged over by 

 the side plates of the ambulacrum, and remains as the so-called linear spiracle 

 (PL XV. figs. 2-4). Some of the hydrospire- slits are excavated in the radials, as in 

 0. pentangularis, though the lamellar tubes into which they lead are more widely 

 separated than in that species (PL XV. figs. 4, 10 ; PL XVII. figs. 13, 14). 



In the typical species of Orophocrinus (0. stettiformis, PL XV. fig. 13) the hydro- 

 spires are entirely concealed by the under lancet-plate just as in Pentremites Godoni 

 (represented in PL XII. fig. 1G), and they open externally by linear spiracles at the 

 sides of the ambulacra (PL XL figs. 8, 9 ; PL XV. fig. 11). The sides of the radial 

 sinus slope downwards towards one another beneath the lancet-plate (PL XVII. fig. 12), 

 and the hydrospire-slits all pierce the substance of the radials just as they do in the 

 Belgian species (PL XIV. figs. 14-18). There are five thin lamellar tubes on each 

 side of the ambulacrum where they descend into the body-cavity; and they may 

 often be found more or less well preserved after removal of the contained matrix, 

 just as in Codaster and Cryptosckisma (PL XIII. fig. 6 ; PL XVI. figs. 3, 4). They 

 are well shown in PL XV. fig. 15 and PL XVI. fig. G. 



In Granatocrinus, Mesohlastus, Cryptoblastns, and Acentrotremites we meet with 

 an altogether different arrangement of the hydrospires from those of the Codaste- 

 ridae ; and it will best be understood after an examination of its simplest form as 



k2 



