26 



F. A. BATHER, CRINOIDEA OF GOTLAND. 



ventral tube; one of the orals, bowever, being perforated by ;m a perture of supposed anal 

 function, determines the posterior interradius. 



From Haplocrinus it is not far to Heterocrinus (texjt-fig. <>). The composition of 

 the cup is precisely the same; but a plate supporting a ventral tube rests in the latter 

 genus on the sloping upper faces of the two posterior radials. This plate is now called 

 the proximal plate of the tube (t) by Wachsmuth ;in<l Springer 1 ): in any case it is homo- 

 logous with the plate x of Pispcrinus, and vvith the plate which Wachsmuth and Springeb 

 called anal» in Symbathocrinus. For my own part I can detect no rnorphological difference 

 between the anal x and the proximal plate of the tube (t), and I believe tliat the proximal plate 

 in the anal interradius is the same rnorphological element in every genus of the Inadunata. 



Calycanthocrinus, the peculiar genus described by Dr. Follmaxx (op. cit.), resembles 

 Pisocrinus, or rather Triacrinus, in its main plan, but has added to its cup tive smaller 

 arm-bearing plates which its describer calls radials. The probable interpretation of this 

 structure is shown in text-tig. 7, where the plates present in Triacrinus are shaded, Ihe 

 added ones being merely outlined. It is noticeable tliat Dr. Follmann did not observe 

 the anal plate in either Triacrinus or Calycanthocrinus, but this may have been due to the 

 ill preservation of the specimens. The sutural surface that supported it is clearly shown 

 by specimens of Triacrinus depressus in the British Museum. 



t ant 



Ant_ 



I p v^v p r.p^ 



Fig. 7. Dissection of Calycanthocrinus. 



Species of the genus. 



The following have been described, 



P. pilula, de Kon. 



P. ornat its, DE Kon. 



P. fiagellifer, Ang. 



P. ollula, Axg. 



P. pocillum, Ang. 



/'. tennesseensis, C. F. Röm. sp. 



P. gemmiformis, S. A. Miller 



P. piriformis, Ringueb. sp. 



P. globosus, Rjngueb. sp. 



P. Benedicti, S. A. Miller 



P. Gorbyi, S. A. Millkr 



P 



canij 



mna, S. A. Miller 



Gotland 



Gotland 

 Gotland 

 Gotland 



England 

 England 



X. America 



N. America 



N. America 



X. America 



X. America 



N. America 



N. America 



') The Perisomic plates of the Crinoids», Proc. Åc. Nat. Sci. Philadelphia, 1890, 

 fig. 8; Feb. 1891. 



PP 



381—384. Pl. X. 



