THE KYDB0SPIRE8 AM) BPIEACLE8. L03 



lacral opening and the proximal enda of the hydrospire-folds jusl beyond it. arc not 

 completely covered by the lancet-plate, as it does not come into such close contact with 

 the deltoids as is represented in Eambach's figure. The Lancet-plate and the deltoid 

 ridge (if long enough) merely form the lateral boundaries of a sinus which is closed 

 distally and converted into an oval opening by the side plates that rest between the 

 edge of the lancet-plate and that of the deltoid. Were there no side plates there 

 would be no hole-like spiracle at all, but a continuous sinus for some little distance 

 along each side of the lancet-plate, very much as in Orophocrinus steWformis 

 (PI. XL fig. 8). This is well shown in PI. I. fig. •"». 



Hambach's omission to notice the share which the side plates often take in 

 forming the spiracle is the more surprising, as he mentioned in his earlier paper 1 

 how they close up the furrow on each side of the lancet-piece. This is less marked 

 in Pentremites Godoni than in P. sulcatus, P. pyriformis, and P. elongates 

 (PL I. figs. 5, 6, 10, 11) ; but we have never seen any Pentremites in which the side 

 plates of the ambulacra are altogether excluded from the distal border of the 

 spiracle, as represented in Hambach's figure 2 . 



"We do not deny that Pentremites exist, such as some varieties of P. Godoni, in 

 which the outward continuations of the spiracular openings beneath the side plates 

 do not lead over the tops of the hydrospire-slits, for these are covered by the under 

 lancet-plate (PI. XII. fig. 1G). On the other hand the spiracles of P. elongatus, 

 P. hemisphericus, and, as we believe, of most, species of the genus, have their distal 

 boundary largely formed by the side plates (PI. I. fig. 5 ; PL XVI. fig. 21). The 

 different ambulacra of the individual which is represented in PL I. fig. vary among 

 themselves in the extent to which the side plates share in forming the spiracles ; but 

 it is evident that when they are removed the spiracle is converted into a long sinus 

 between the lancet-plate and the deltoid. This individual is remarkable in another 

 way ; for three of the spiracles are rendered double by the great development of the 

 deltoid ridge or oral crest, which is often not visible at all in this species, owing to 

 the side plates meeting above it as shown in fig. 4. The spiracles thus come to 

 have the same character as those of Pentremites Burlingtoncnsis, which is placed by 

 Hambach 3 in the same group as Cryjttoblastus inch (PL VII. figs. 14, 15), 



1 Trans. St. Louis Acad. Sci. 18S0, vol. iv. no. 1, p. 150. 



-' We beg to apologise to ilr. Hambach in advance if we have misinterpreted his diagrammatic figure 

 of Pentremites sulcatus. It has given us a great deal of trouble. For he affords no explanation of the 

 meanings which he intends to convey by the various depths of shading which he employs, except to say 

 that the sinus " is so surrounded by the zigzag plated integument that two of the so-formed openings appear 

 externally only as one " ; and that " By a and 6 is the covering integument removed to show the sutures 

 between (a) deltoid and (b) lancet pieces." These sutures, however, arc equally plain in every part of tho 

 figure, and so we are quite at a loss to understand the meaning of tho above remark. There are also ten 

 large openings, not five, besides the anus, and the two of each interradial pair are represented as separated by 

 a wide striated partition which passes our comprehension altogether. 



3 Trans. St. Louis Acad. Sci. 1884, vol. iv. no. 3, p. 545. 



