140 SMITHSONIAN INSTITUTION 



PLATE LXVII 



The Ventkal Structures of Onychocrinus 



(All figures natural size except where otlierwise stated) pace 



Figs. i-io. Onychocrinus ulrichi Miller and Gurley 425 



(Also on Plates XXI, LXVI and LXVIII) 



Fig. I. Dorsal view of a specimen showing infrahasals in place, form of posterior basal, and anal 

 tube. 



2a. Ventral view of specimen with tegmen preserved and partly in place. 



2b. Central part of same, enlarged. The finely plated integument or perisome is well pre- 

 served, although displaced ; some ambulacra, with their long alternating plates, can be 

 seen coming in from the rays. The orals, with the large posterior one and the strong 

 supporting plates leading along the posterior ambulacra in place, and the anal tube 

 with the folded perisome attached to it, are beautifully preserved. It can be readily 

 seen from this specimen that if the tegmen were lifted to its proper height, this row 

 of strong articulated anal plates would form a firm but pliant support for a fold or 

 groove in the perisome constituting the rectum. X 2. 



3(7. Similar specimen with the anal series of plates lying behind the posterior oral, and 

 attached as far as the distal end. 



3&. Detail of distal end of tube and contiguous parts, enlarged and drawn from a different 

 angle. X 2. 



4. Posterior basal and anal tube from another specimen, showing the manner in which the 



perisome is attached to the ventral margin of the plates. At the upper part, where 

 the tube is fallen over to the right, the perisome has slipped away from the plates, 

 and the sloping groove at their margin by which it was attached is plainly seen. X 2. 



5. Inner side of detached anal series from another specimen near the distal end, with the 



folded perisome attached forming a tube, now flattened by pressure ; a, cross-section 

 of plate and perisome. X 2- 



6. Inner lateral view of part of a tube (of O. exsciilptus) showing the sloped and grooved 



margin for attachment of perisome. X 2. 



7. Ventral view of a specimen with tegmen almost perfectly preserved. Shows the peri- 



some, ambulacra and oral plates in position. The anterior and lateral orals (one 

 being pushed in under another and scarcely visible in this view) form a pyramid 

 meeting the smaller end of the enormous posterior oral. The ambulacra enter 

 between the orals, which evidently were opened or closed at will ; the two posterior 

 ambulacra follow the edge of the posterior oral and are further supported by plates 

 partly seen at the left, but which are better shown in fig. 2&; the posterior oral is per- 

 forated, and exceptionally in this specimen is transversely divided. The anal tube is 

 but little exposed here, lying under the edge of the oral. 



8. View of the under side of the same structures in another specimen, seen from the dorsal 



side, with the calyx plates removed. The open space where the ambulacra converge 

 into the oral pyramid is shown. 



ga. The oral plates and adjacent perisome in another specimen, showing perforation of the 

 posterior oral. The small orals are not well exposed here, and a foreign object lies 

 next to them at one side. X 4- 



g6. Detail of same, showing relative size of pores. X 8. 



ID. Another specimen with the complete tegmen preserved ; the anal tube is in its usual posi- 

 tion turned to the right and behind the oral. 



Figs. II. Onychocrinus diversus M. and W 423 



(Also on Plate LXV) 

 Fig. iia. Calyx of a specimen from Burlington, with rays broken ofif, and all tegminal and anal 

 structures removed. Posterior view, showing the exact form of post. B, with socket 

 for support of anal tube half way down the outer side and to right of middle, the 

 distal margin not being indented for its reception. 

 11&. Ventral view of same. Shows distal margin of post. B thinned to a sharply rounded edge, 

 with no face for sutural attachment; also similar condition of adjacent brachials. 



Unless otherwise stated, Keokuk Gr. : Lower Carboniferous. Indian Creek, Indiana. 

 All specimens figured on this plate are in the author's collection. 



