54 CATALOGUE OF THE BLASTOIDEA. 



distinctly above the level of the linear impression which represents the mould of the 

 under surface of the lancet-plate. Hambach x gives a general description of this plate 

 as having a longitudinal groove on its under surface ; and one would therefore expect 

 to find an impression of this groove in the mould of the under surface. It is, how- 

 ever, perfectly even from side to side, and entirely without any trace of the duct or 

 vessel which Hambach mentions. We are inclined to think that his description is 

 too general, and only applies to Pentremites proper, in which type the ambulacra are 

 different from those of Granatocrinus. But we are certain of two points. There is 

 no duct beneath the lancet-piece of Granatocrinus Norwoodi, and no other oral ring 

 than the very complex one which unites the canals within the lancet-plates, as shown 

 in PI. VI. fig. 19. If this, as we have every reason to believe, was the structure 

 which Hambach obtained entire in Granatocrinus Norwoodi, we are surprised that he 

 did not think of correlating it with the canals within the lancet-plate which he 

 described in the same paper. It will be quite time enough to think about a second 

 oral ring connecting the longitudinal ducts beneath the lancet-pieces when the pre- 

 sence of these ducts shall have been satisfactorily demonstrated ; but this is far from 

 being the case at present, as pointed out above. 



The complex structure of the oral ring, as preserved in Granatocrinus Norwoodi, is 

 very remarkable, and has puzzled us considerably. We have seen no trace of any- 

 thing of the kind in ground preparations of the summit of any Blastoid, not even in 

 Granatocrinus itself; and we are also in some doubt as to the functions of this ring. 

 But the discussion of this subject had better be postponed. 



There are two different types of Blastoid in which we have found a peculiar modi- 

 fication of this lancet-canal. Both in Schizoblastus Sai/i and in Troostocrinus (?) lineatus 

 we have found the lancet-plate to contain three canals instead of one (PL XVII. 

 figs. 1, 18). These are disposed at the angles of a triangle, the apex of which is 

 downwards ; so that the lower canal is just beneath the middle of the interval between 

 the other two. We have been unable to get a satisfactory section of an ambulacrum 

 in any other species of Schizoblastus ; and in the section of Troostocrinus Heinwardti, 

 which is shown on PL XVII. fig. 17, the nature of the lancet-canal is not clear at 

 all ; so that we have no opportunity of judging how far this triple perforation of the 

 lancet-plate is a character of any generic value. At any rate it is worth notice that 

 although so different in external form, Troostocrinus and Schizoblastus are closely 

 allied in the structure of the spiracles. 



B. The Superficial Masking* of the Lancet-flate. 

 The median line of the upper surface of the lancet-plate is occupied by a fine 

 groove (PL I. figs. 1-6, 9-11), which appears to be universally recognized as corre- 



1 Trans. St. Louis Acad. Sci. 1880, vol. iv. no. 1, pp. 149, 151. 



