DESCRIPTIONS OF THE 8PECIE8. 197 



lit marks. We have already Been that Troostocrinus approaches the Pentremitida 

 through Pentremitidea Paillettei. Metablaatus and Triccelocrinua on the other hand 

 have much resemblance in the general structure of their spiracles, both to the 

 Nucleoblastidse, and to some forms of Orophocrinus, as we have explained on p. 1 10. 

 But the_y altogether differ both from these Blastoids and from one another in the form 

 of the calyx. In this respect Metablastus resembles Troostocrinus, the basals and 

 radials of both genera being very much elongated and the ambulacra verj narrow 

 (PI. V. figs. 21, 22 ; PI. XII. tig. 11). We have no specimens of Troostocrinus 

 Reimoardti which are perfect enough to show the constriction at the lower end of 

 the basal cup which is figured by Koemer. But there is nothing like it in any 

 species of Metablastus that we have seen, even in M. lineatus, in which the base is 

 less markedly trihedral than in forms like M. WachsmutM and others. The five 

 sides of the radial portion of the cup pass gradually downwards into the three sidr> 

 of its basal portion in the manner described on pp. 16-18 l . The two strong ridgi 8 

 which start from the lips of radials A and B approach one another below and unite 

 into a single median ridge on the azygos basal. This forms one edge of the trihedral 

 base, while the other two are the strong ridges on radials C and E, that on radius D, 

 which is the weakest of all, gradually dividing and dying away below. This struc- 

 ture is shown very well in the basal cup of the specimen of which the summit is seen 

 in PI. XVIII. fig. 15, and we believe it to be eminently characteristic of Metablastus. 

 It can be traced in M. lineatus, which rather resembles Troostocrinus Urinwanlti in 

 the elongate and tapering form of the basal cup, while the three ridges are extremely 

 prominent in the shorter and more flattened base of Triccelocriuus (PI. XVI. figs. 17, 

 IS; PI. XIX. tigs. 13, 14). They are also very well marked in the long basal cup 

 which has been noticed by Munier-Chalmas and by Oehlert under the name L'c/u- 

 crinus Cottaldi, and it is chiefly for this reason that we formerly referred it to a 

 species of Troostocrinus (PL V. fig. 22) 3 which name must now be changed into 

 Metablastus, though it is of course possible that an entire calyx may eventually be 

 discovered with different summit-characters from those of this genus. 



The morphology of the spiracles of Metablastus, and their relations to those of 

 Orophocrinus and Schizoblastus, has been described on pp. 109-111. In the type 

 species, both of the latter genus and of Metablastus, the lancet-plate is triply per- 

 forate (PL XVII. figs. 1, 18), though we do not know how far this is the case in 

 other species. The same may be said of the hydrospires of Metablastus, which are 

 quadruple in M. lineatus (PL XVII. fig. 18); but we have no sections of them in 

 any other species. 



The ambulacra! pinnules are known in three species of Metablastus, having been 



described by White in M. lineatus, and figured in M. Varsouviensis by Meek and 



Worthen, while they are also preserved in one of Wachsmuth's specimens of 



M. Wortheni (PL III. fig. 13). There are some suspicious-looking lines on the 



1 The name Metablastus should now be substituted for Trocstocrinns in this description. 



