DESCRIPTIONS OF THE SPECIES. 205 



By the kindness of Professors A. Gaudry and E. Perrier, of the Museum d Hi toire 

 Naturelle at Paris, we have been enabled to figure an excellent specimen of what 

 appears to be TricoelocHnua W6odmam(Pl. XIX. figs. 13-15). It has also been 

 figured by Prof. Gaudry himself 1 under the name " Pentremites du groupe de 

 /'. Wbrtheni," in a radial view which shows the bifurcation of the median ridge at the 

 lower end of radial D. The part of the plate enclosed within this bifurcation is all 

 that he considers as the radial, while the rest of the body of the plate and its limb 

 on either side are regarded as interambulacral pieces. We think, however, that Trot'. 

 Gaudry would scarcely have come to this conclusion it' he had examined one of the 

 other radials (C or E), in each of which the median ridge is continued straight down 

 into an angle of the trihedral base (PI. XIX. figs. 13, 14). The analogy of the 

 radials of other Blastoids shows very clearly that their limbs cannot be regarded as 

 interambulacral pieces, though we are quite disposed to agree with him in his view 

 of the plates which he marks "aires interambulacraires " in Eheaeriiiiis-, as will be 

 evident from what we have said on pp. 28, 29. But these plates in Elceacrinus are 

 parts of the deltoids, and altogether different in character from the radial limbs of 

 Pentremites or Triccelocrinus, though occupying the same position as regards the 

 ambulacra. 



There is another point in Prof. Gaudry 's figure of T. Woodmani about which we 

 regret to have to differ from him. For it shows small deltoid pieces appearing 

 externally above the truncated ends of the radial limbs just as in the figure of Pen- 

 tremites sulcatus on the same page. We had returned the specimen to him before 

 his book was published, and we therefore had no opportunity of comparing it with 

 his figure ; but so far as our own observations of it are concerned, we believe that 

 the radial limbs extend right up to the summit and overlap the deltoid plates, as 

 shown in PI. XIX. figs. 13, 15. 



The ambulacra of Tricaelocrinus are generally longer, and extend farther down the 

 radials than those of either T roost oerinus or Metablastus, and for the greater part of 

 their length the hydrospires beneath them are cut off from the body-cavity by exten- 

 sions of the radial plates which close the sinuses below, i. e. the distal part of the siuus 

 is not deep enough to penetrate through the thickness of the radial plate. We 

 have already described this condition in three species of Pentremites (PI. II. figs. 

 13, 31 ; PI. III. figs. 4-12 ; PI. XVIII. figs. 7, 8). But it is carried to a much greater 

 extent in Tricoelocrinus, so much so as to afford a character of considerable systematic 

 value. It is very well shown in the large isolated radials of Tricxlocrinus obliquatus, 

 Roemer, sp., which we take to be different from the species described under that 



1 Les Enchainementa du Monde Animal duns Lea Temps Geologiques. Fossilcs Primaires (Paris, 1SS3), 

 p. 89, fig. .37. 



2 Ibid, pp. 00, 91, fig. 60. 



3 See Chapter V. p. 95. 



