HAMBACH STRUCTURE A- CLA«;SIFICATION OF PENTREMITES. 539 



drospiric sacs for the passage of this duct to facilitate a connec- 

 tion with the oesophageal ring underlying the annulus centralis. 

 The hydrospiric sac runs from the apex of the ambulacral field 

 to the summit, where it terminates ; its plicas rest in correspond- 

 ing plicas of the plicated lateral expansion of the deltoid piece, and 

 do not unite into one tube with the adjoining ones as described 

 and figured by Billings.* The shape in which these hydrospiric 

 plicas are found, as well as the difterence in color between them 

 and the adjoining opaque calcareous substance of the shell, to- 

 gether with the physiological function ascribed to them (respira- 

 tory according to Billings), denote the once elastic nature of these 

 organs as well as of the tentacles, which communicate with the 

 hydrospiric sac through the poral openings, and not with any 

 ovarian tube as Mr. Carpenter tries to misrepresent my statement. 

 They form in their collapsed state the supplementary poral plates 

 of Roemer, which, to the great surprise of Mr. Carpenter, are 

 actually found preserved in an open condition from the Carbonif- 

 erous period to the present time. Neither do I ignore any facts 

 given by Rofe, Billings, Wachsmuth, or others, if they prove to 

 be such ; but in this case the marginal pores along the ambula- 

 crum do not lead into an ovarian tube, as stated above. 



Likewise is the zigzag plicated integument preserved which 

 covers the ambulacral field, incredible as this may seem to Mr. 

 Carpenter, whose incredulity however is no evidence to the con- 

 trary. Roemer's figure and description of Pentremites crenu- 

 latus do not contradict my statements, as the Doctor does not say 

 anything in regard to this crenulation in particular ; but, on 

 the contrary^ the ambulacral field which is marked £ in Roe- 

 mer's Fig. 2 on Plate I. of his " Monographic der Blastoideen" 

 indicates the existence of a layer or integument covering the same 

 (although not described as such). The sutures, or at least the 

 longitudinal sutures between lancet and foral pieces, would be 

 visible if it was only a surface ornamentation of the calcareous 

 shell as supposed by Mr. Carpenter, which is however not shown 

 in the figure cited, nor is this suture visible in entirely well pre- 

 served specimens, of which I possess more than one in my col- 

 lection. Still more, I have specimens where a partial compres- 

 sion of an ambulacral field has taken place, causing a distortion 



* Loc. cit. p. 102, Fig. 60. 

 i V — 3 1 [Apri* 18, 1S84. 



