1883.J On a New Crinoid from the Southern. Sea. 



139 



basals, and, with one exception, terminate in a free edge at the margin 

 of the disk. The exception is the interradial of the anal side, which 

 bears a short and tapering armlike appendage of five or six joints. It 

 has no special relation to the anal tube, the lower part of which, like 

 the peripheral portion of the disk, bears a pavement of anambnlacral 

 plates. But the centre of the disk is occupied by a relatively large 

 and substantial oral pyramid, so that the disk in its general aspect 

 resembles that of Hyocrinus. 



Thaumatocrinus is thus distinguished by four striking peculi- 

 arities : — 



(1.) The presence of a closed ring of basals upon the exterior of 

 the calyx. 



(2.) The persistence of the oral plates of the larva, as in Hyocrinus 

 and Phizocrinus. 



(3.) The separation of the primary radial s by interradials which rest 

 on the basals. 



(4.) The presence of an arm-like appendage on the interradial plate 

 of the anal side. 



Taking these in order — 



(1.) ISTo adult Comatula, except the recent AtelecHnus and some 

 little known fossils, has a closed ring of basals ; and even in Atele- 

 crinus they are quite small and insignificant. 



(2.) In all recent Com atulce, in the Pent acrinidce and in Bathycrinus, 

 the oral plates of the larva become resorbed as maturity is ap- 

 proached. In Thaumatocrinus, however, they are retained, as in 

 Hyocrinus, Phizocrinus, and Holopus, representatives of three different 

 families of Neocrinoids. 



(3.) There is no Neocrinoid, either stalked or free, in which the 

 primary radials remain permanently separated as they are in Thauma- 

 tocrinus, and for a short time after their first appearance in the larva 

 of ordinary Crinoids. The only Palaaocrinoids presenting this feature 

 are certain of the Phodocrinidce (as understood by "Wachsmuth and 

 Springer), e.g., Peteocrinus, Phodocrinus, Thylacocrinus, &e. In the 

 two latter, and in the other genera which have been grouped together 

 with them into the section Rlwdocr miles (W. and S.), there is a 

 single interradial intervening between every two radials, and resting 

 on a basal just as in Thaumatocrinus. But in the Lower Silurian 

 Peteocrinus (of Billings ; emend W. and S.) the interradial areas 

 contain a large number of minute pieces of irregular form and 

 arrangement. 



(4.) It is only, however, in Peteocrinus, and in the allied genus 

 Xenocrinus, Miller, which is also of Lower Silurian age,* that an anal 

 appendage similar to that of Thaumatocrinus is to be met with. 



* Reteocrinus occurs in the Trenton Limestone of Ottawa and in the Hudson 

 Eiver G-roup of Indiana and Ohio. Xenocrinus has as yet been found in the latter 



