46 UmTACKINUS: ITS STRUCTURE AND RELATIO]N-S. 



sidered as the anal opening. He notes the fact that the opening which 

 he takes to be the mouth is very excentric in position. 



This* observation of von Koenen is of the utmost interest, as it is the 

 first indication we have of the actual position of the mouth in the later 

 Fistulata, and is the nearest approach to the disk structure of Uintacrmus 

 that has yet been found in any fossil. Whether the supposed ambulacral 

 furrows were covered by plates cannot be ascertained from the description, 

 and is probably not discoverable in the specimen. 



On Wagner's other specimen {Op, cit. 1891, Fig. 1) he also found an 

 opening which he considers to be the anal opening. 



In the same paper von Koenen gives some important information as to 

 the disk of Dadocrinns. In two specimens of D. gracilis, somewhat crushed, 

 he succeeded in partially freeing the tegmen, which he found entirely calci- 

 fied, but which had been pliant, composed of small irregular plates, largest 

 in the middle. This plated integument extended downward in two inter- 

 radial areas as far as the second radial, and at the top terminated in a blunt 

 point containing a small opening. From this opening the plates run down- 

 ward in oblique rows, increasing rather rapidly in width until they pass 

 into the plates in the central part of the tegmen. Of that opening he 

 says : " The opening appears not to have been located centrally, and it 

 may therefore well be considered as the anal opening. Of mouth and 

 anbulacral furrows I have not been able to observe any trace." 



Von Koenen thinks Holocrinus is to be compared with the Apiocrinidge, 

 among w^hich a similar high ventral sac has been observed ; w^hile he 

 regards Dadocrinns as related to older forms such as ErisocrinitSy rather 

 than to Encriniis. 



Dr. Jaekel^ has described a very interesting specimen of Encrinus 

 Carnalli^ exhibiting the tegmen, which is a thin pavement of very small 

 plates. The mouth and ambulacral furrows are not visible, but there is a 

 well-preserved anal tube, which rises free as a short sac, composed of finger- 

 like folds laid together and surrounding the anal opening. These folds are 

 not plated. What the exact position of this tube is, relatively to the centre 

 or margin of the disk, is not disclosed, either by the description or figure. 

 In this paper he also refers to the tegmen of Holocrinus as composed — 

 especially in the middle — of relatively large plates, of irregular, rather 

 long oval form ; and he states as to Dadocrinns, that while its tegmen has 



* Sitzungsberichte der Ges. Naturf. Freunde zu Berlin. Jahrg. 1894, Nr. 6, p. 155. 



