TllK \MP.ri \< l: \. ib 



This plate seems to have altogether escaped the notice of Roemer, who figures the 

 hydrospires of Pentremites Oodoni as lour on each side l , all completely visible after 

 removal of the lancet-plate, which doubtless brought away the under lancet-plate 

 with it. Wachsmuth and Springer give a diagrammatic figure 2 of its relations in Pen- 

 tremites, the species illustrated, though not named, being one in which this plate is 

 narrow, and only occupies the middle of the radial sinus. It is called the " inner 

 lancet-plate," and is said to have a tubular passage running lengthwise through it, 

 whilst the lancet-plate is figured in section as altogether imperforate. 



Hambach 3 , however, states that the lancet-plate of Pentremites sulcatm contains 

 a minute longitudinal canal, and he describes its inner face as "concave, semilunar, 

 and grooved in its whole length for the reception of some duct or vessel ;" while, 

 according to lloemer 4 , the lancet-plate on its inner face is "zu einer flachen Liings- 

 rinne ausgehohlt." He gives no figure showing this groove, but Hambach s does, and 

 from a comparison of Hambach's figure with our own dissection of a Pentremites- 

 ambulacrum we are inclined to think that this longitudinal furrow of the laucet-piece 

 is merely the impression of the prismatic ridge on its under surface which we have 

 described above. Our supposition that this prismatic ridge is the duct or vessel which 

 Hambach mentions as lying beneath the lancet-piece, seems the more probable 

 because he says G that " the calcareous substance which is frequently found to fill out 

 the duct, or the upper blade of the hydrospiric sac, which is smooth and overlies the 

 plicas, may mislead to the supposition of having here a sublancet-plate." It may be 

 noted too that in his figure of a restored ambulacrum, on the same page, this duct is 

 represented as a plate of the same solid nature as the pore-plates, without any indi- 

 cation of perforation such as he gives for the " canal perforating " the lancet-piece. 



We cannot therefore confirm Hambach's description of any duct, vessel, or canal 

 beneath the lancet-plate of Pentremites ; and we are strongly inclined to believe that 

 he is in error when he describes this duct as " resting in the concave furrow of the 

 lancet-piece, and running from the apex of the ambulacral field to the summit, where 

 it connects with a circular duct [oesophageal ring ?] surrounding, on the interior side, 

 the central orifice or annulus centralis. This I have been so fortunate as to obtain 

 entire from a well-preserved specimen of Pentremites Norwood) '; though, being 

 probably composed of a very fine and delicate tissue or membrane, it is destroyed in 

 most cases, and therefore very rarely observed" \ 



1 Archiv f. Naturgesch. 1851, Jahrg. xvii. lid. i. Taf. i. fig. 3. 



2 " Eevision of the Palseocrinoidea," Part I. pi. iii. fig. 4. 



3 Trans. St. Louis Acad. Sci. 1880, vol. IT. no. I, p. 1 in. 

 * Archiv f. Xaturgesch. 1S51, Jahrg. xvii. Bd. i. p. 333. 



5 Trans. St. Louis Acad. Sci. 1880, vol. iv. no. 1, pi. A, fig. 9. 

 « Ibid. No. 3, p. 532. 

 ' Ibid. No. 1, p. 151. 



