the Morphology of the Blastoiclea. 219 



ments about it arc somewhat obscure. He says that ho lias 

 been so fortunate as to obtaui this structure entirely from a 

 well-preserved specimen of Pentremites (i. e. Granatocrini/^) 

 Noricoodij but tluxt it is connected with tlie longitudinal duct 

 or vessel beneath the lancet-piece. As, however, no second 

 subarabulacral canal has been detected in this species cither 

 by Messrs. Wachsmuth and Springer or by ourselves, we 

 cannot help suspecting that Dr. llambach must have seen 

 the " longitudinal duct " in a Pentremites and the " circular 

 duct" in Granatocrimis Norwoodi] but, in default of further 

 information, we cannot absolutely identify this " circular 

 duct" with the oral ring described above. 



Messrs. Wachsmuth and Springer* have suggested that 

 " the passage directly beneath the (ambulacral) held is pro- 

 bably the dorsal or axial canal [L e. of the Crinoid arm), 

 which by the inverted position of the arms became the inner 

 instead of the outer passage." We are not sure that we 

 quite understand Mr. Wachsmuth's theory of the ambulacra 

 of the Blastoids. If they represent tire inverted arms of a 

 Crinoid, surely the food-grooves ought to be internal and not 

 external. But if by this and similar expressions Mr. Wachs- 

 nuith means to describe a Blastoid ambulacrum as a Crinoid 

 arm partially bent upon itself, we are disposed to agree with 

 him. 



It is probable enough that the Blastoids possessed a cham- 

 bered organ and axial cords radiating from it, as in the 

 Crinoids ; but we do not think that these cords were lodged 

 within the lancet-plates or underlancet-plates of the ambulacra, 

 as supposed by Wachsmuth and Springer. 



We propose to limit the name Pentremites to those Blas- 

 toids which resemble P. Godoni, Defr., P. sulcatus, llijmer, 

 and P. pyriformis, Say, in their structure and general appear- 

 ance. The ambulacra are broad and petaloid ; and in most 

 species the side* plates merely rest against the edges of the 

 lancet-plate, without covering any part of it. The central end 

 of each oral plate is flat and laterally expanded, with a more 

 or less marked oral ridge in the middle line tiiat divides it 

 into two lateral halves. Each arm forms the floor of a passage 

 leading along the lower part of the radial sinus over the upper 

 ends of the hydrospire-slits. It is converted into a canal (the 

 hydrospire-canal) by the side plates, Avliich arc Avedged in 

 between the lancet-plate and the side of the radial sinus. 

 Those nearest the centre may either meet one another over the 



* Uevisiou, part ii, p. 3u (207), 



