52 CATALOGUE OF THE BLASTOIDEA. 



writing two years later 1 , describes it as " nothing more than a fissure between two 

 hydrospiric sacs for the passage of this duct 2 to facilitate a connection with the oeso- 

 phageal ring underlying the annulus centralis" It will be evident from all our 

 figures that this " ambulacral opening " is in the line of the interdeltoid suture, and 

 entirely independent of the hydrospires at the side of the under lancet-plate ; for these 

 might be removed altogether without affecting its boundaries in the least. It lies 

 exactly beneath the central end of tire canal within the lancet-piece, and is in fact the 

 very opening which Hambach describes as perforating a deltoid " transversely about 

 midways," and as serving for the passage of this canal to join the oral ring. 



We quite believe that the canal within the lancet-piece descended through this 

 opening beneath its central end on its way to join the oral ring. At any rate this is the 

 inference which we should draw from the study of preparations of typical Pentremites 

 like those shown on PL XII. figs. 15, 17, where the radial extensions of the central 

 ring occupy the lines of suture between two deltoid pieces. Hambach agrees with us 

 in regarding this ring as formed by the junction of canals within the lancet-plates 

 which leave them through the little processes beneath their central ends ; but he goes 

 on to describe these radial canals as passing through the middle of the deltoid pieces, 

 which would give them an interradial position. On the other hand, he describes this 

 same opening between two deltoids, or, as he puts it, between two hydrospiric sacs, 

 as serving for the passage of the duct beneath the lancet-piece on its way to join 

 another oesophageal ring. But he gives no description of the relations of this second 

 ring to that joining the lancet-canals, which is so easily demonstrated by grinding 

 down a good specimen (PL XII. figs. 15, 17). He tells us, however, that he has 

 obtained this second ring entire from a well-preserved specimen of Pentremites 

 Norwoodi. But we should like to know on what grounds he regards the structure 

 which he has found in Granatocrinus (not Pentremites) Norwoodi as the annular 

 centre of a vessel lying beneath and not within the lancet-pieces. It may be that he 

 changed his views since the publication of his first paper ; but he nowhere gives any 

 hint of his having done so, and in fact his second paper contains definite references 

 to two distinct rings. So far as we can make out, however, he has not seen the two 

 rings in any single specimen, but has obtained sections of Pentremites showing the 

 ring uniting the lancet-canals (PI. XII. figs. 15, 17); while he has found what he 

 takes to be an altogether different structure in a well-preserved example of Granato- 

 crinus Norwoodi. If the lower ring is entire in this fine specimen, some traces of the 

 upper one should surely be visible as well. But Hambach says nothing about it, at 

 which we are not surprised ; for we have a very strong suspicion that the structure 

 which he has seen in Granatocrinus Norwoodi is nothing but a cast of the ring uniting 

 the canals within and not beneath, the lancet-pieces. 



1 Trans. St. Louis Acad. Sci. 1884, vol. iv. no. 3, p. 53S. 



1 I. e, the one which llumhaeh supposes to lie beneath, not in, the lancet-plate. 



