BASAL PLATES IN CRINOIDEA CAMERATA 673 



Let us now turn to a study of the specimen of Teleiocrinus 

 umbrosus (PL I, Nos. 1, 2, 4, 6) by which Wachsmuth and Springer 

 thought their theory to have been confirmed. Upon careful exam- 

 ination of this specimen grave doubts have arisen in the writer's 

 mind concerning the validity of its assigned orientation. Teleio- 

 crinus umbrosus has a central anal tube; therefore use of this as a 

 reference point for orientation is denied. If, however, we consider 

 that the interray in which the abnormality (loss of the anal plate) 

 occurred should perhaps show some variation from the supposedly 

 normal interrays, a different answer to the problem is obtained. 

 Four of the interrays in this specimen show the normal Teleiocrinus 

 umbrosus type of development: 1, 2, 2, 2. The fifth interray shows 

 the following arrangement: 1, 3, 4, 2, which varies from the normal 

 posterior interray (A, 2, 3, 4, 2) or (A, 2, 4, 3, 2) by the loss of but 

 two important plates — the anal plate and one plate of the super- 

 imposed pair. There is here too close a parallel to be considered 

 entirely accidental, and it does not seem unreasonable that if some 

 plates are missing from an interray, that interray should show signs 

 of abnormality. If, then, it be assumed that the abnormal interray 

 in this specimen of Teleiocrinus umbrosus is the true posterior 

 interray, the basal formula is not ab — c — de — , as in,Platycrinus, 

 but ab — cd—e — , for the simple basal is bisected by the plane of 

 the right-posterior interray. 



Let us, before going farther, examine the specimen of Stegano- 

 crinus pentagonus (PL II, No. 15; PL III, Nos. 1, 2) which, like the 

 specimen just described, has lost its anal plate. Steganocrinus 

 pentagonus , unlike Teleiocrinus umbrosus, has a slightly eccentric 

 anal tube; the vertical convexity of the posterior interray is much 

 flatter than in the other interrays, and the interbrachial plates are 

 ornamented at a lower level by low sharp nodes. If, then, this 

 specimen be oriented according to the position of the anal tube, 

 convexity of interrays, and ornamentation, the basal formula is 

 found to be, not ab — c — de — , as in Platycrinus , but b — cd — ea — , for 

 the simple basal is bisected by the plane of the left-posterior 

 interray. In Teleiocrinus umbrosus the posterior basal has anchy- 

 losed with the left-posterior basal; in Steganocrinus pentagonus it 

 is anchylosed with the right-posterior basal. The reversion herein 



