Hambach — Revision of the Bbtstoideae. 



17 



It is not often found preserved, at least not in an open 



condition, but oftener in a collapsed condition. In this 



condition it presents the so-called underlancet plate of late 



authors.* I can prove the existence of this vessel by a 



number of cross sections of an ambulacrum of which Fio-. 8 



and Plate II. are a correct representation. Lancet piece and 



poral pieces are well preserved, also the vascular duct a, 



which in this specimen is tilled with 



calcspar which could enter only in a 



liquid state. The triangular space b 



at each side of the vessel is filled 



by a kind of clayey substance, which 



must also have been in a very plastic 



or liquid form when entering the 



cavity. Underneath we have the 



hydrospiric plications c. Had the 



vessel a not existed the substance 



in b would have undoubtedly filled 



the whole space if it were the 



first to enter the calyx. On the 



other hand if the liquid calcspar 



had entered first it would have 



spread over the whole space if no 



vessel had existed. The walls of 



these vessels must have been very 



thin, which accounts for their easy destruction and absence in 



most cases. In an empty state they would naturally have 



collapsed, but nevertheless could easily be distinguished from 



the underlying upper blade of the hydrospiric tube, in not 



showing a suture line in the center, which would be the 



case if the vessel had been destroyed and the upper blade 



of the hydrospiric tube were exposed to view. 



Fig. 8. 



a. Water vascular duct. 



b. Space at each side of duct 

 fllled with clayey sub- 

 stance. 



c. Lobes of the hydrospiric 

 tube. 



d. Upper blade of the hy- 

 drospiric tube. 



e. Nervous channel. 



f. Tentacle. 



g. Ovarian tubes, 

 h. Lancet plate. 

 1. Poral pieces. 



THE HYDR08PIRES OR RESPIRATORY ORGAN. 



The hydrospires in the typical species like Pentremites sul- 

 catus, Jlorealis, iiyriformis, etc., form ten isolated plicated 



* Eastman. Text Book of Palaeontology, Vol. I., p. 19L 



