INDIANA PALAEONTOLOGY. m. 



anal opening, closing in above the lower covering. Both the outer and inner 

 integuments are very delicate structures, thin as the thinnest sheet of writing 

 paper. At the re-entrant angles are inner knife-edge-like strengthening, up- 

 right partitions that may or may not extend to the center, separating the inner 

 continuation of the spiracles. Thus tiie pyramid seems to cover a stellate space 

 of five radiating tunnels, extensions of the spiracles and anal opening. Whether 

 they unite at the center, can not be dt-finiteU* determined, neither can it be 

 learned whether there is any communication between this chamber nnd the out- 

 side or any perforations through the lower integument. The direct communica- 

 tion between the visceral cavity and the outside by means of the tunnels leading 

 to the ambulacral grooves can be plainly seen. 



The outside surface of the pyramid shows evidences, apparently, of being 

 made up of small plates, but we can not say positively. When one takes into 

 consideration the great difficulty even in tracing the sutures of the radials and 

 deltoids in well preserved, silicified Pentremites from the Kaskaskia Limestone, 

 there is no wonder that the structure of these delicate ventral integuments 

 should escape him. 



Why the spiracles or the anal opening or both should be cut otf from exter- 

 nal communication is not apparent, but if it is so, as appears almost certain, we 

 should accept the fact whether it is consistent with our conclusions as to the 

 "eternal fitness" of things or not. Too, our conclusions may be based on erro- 

 neous reasoning, after all. Again, that specimens preserving these ventral cov- 

 erings should be so scarce is not at all surprising taking into account their very 

 delicate character. In a score of years collecting from the Burlington Lime- 

 stone here at Louisiana, during which time several hundred specimens of Dicho- 

 crinus have passed through our liands, we have yet the first one to find with the 

 ventral covering intact, despite the fact it has been seen and figured, time and 

 again. Should we reason from ou/' experience we could assert that the ventral 

 side of Dichocrinus is never closed b}' a disk of covering plates and yet we 

 would be in error. 



Strange as it may seem, in the very same locality where a perfect body of 

 Dichocrinus has never yet been found, a very large per cent of the specimens of 

 Schlzohlaiitus saiji preserve the delicate ventral covering and. in this connec- 

 tion, we may say it is unlike that of Pi'itfrcinifes (/odoni in that it is not 

 double, corresponding to the inner roofing in that species and yet covering the 

 spiracles, but never the anal opening so far as we have been able to see in the 

 study of dozens of well preserved specimens. 



In a single beautifully preserved individual of Orophocr'tnHS steJlitorm».s 

 from the same place, the narrow rounded ridges of minute plates that cover the 

 ambulacral grooves, extend some distance down four of the ambulacra and to 

 the very distal end of the fifth. 



