BASAL PLATES IN CRINOIDEA CAMERATA 507 



are possible: abc — d — e — , a — bed — e — , a — b—cde — , b — c — dea — , 

 and c—d — eab — . Of these combinations one, the abc — d — e — 

 combination, is found in Zophocrinus, as figured. This orientation 

 does not agree with Bather's interpretation of the genus, 1 but is 

 based upon the discovery of the anus in a large number of speci- 

 mens studied by the writer in the Springer and Walker Museum 

 collections. 



Fig. 5, No. 4, shows the anchylosis of four adjacent plates 

 (abed — e — ), leaving but one free plate. Here, however, any plate 

 of the five might have been the free plate, and five combinations 

 are possible: abed — e — , a — bede — , b — cdea — , c — deab — , and 

 d — eabc — . Of these combinations none have been discovered. 



Fig. 5, No. 5, illustrates one of five possible combinations in 

 which only one suture exists (abede — ). Combinations 4 and 5 

 seem too asymmetrical from a structural viewpoint to occur as 

 either generic or specific characters, but might appear in cases of 

 delayed anchylosis, in which complete anchylosis is the normal 

 result. 



Fig. 5, No. 6, illustrates the simple tripartite combination 

 (ab — c — de — ), in which two pairs of basals are anchylosed. Of 

 the five possible combinations of this type four are now known: 

 a — be — de — , in Allagecrinus americanus; 2 b — cd — ea — , in Stor- 

 thingocrinus 3 and Hyocrinus (No. 6, a) 4 ; ab — c — de — ,m.Sybathocrinus 

 and the Platycrinidae (No. 6,b); be — d — ea — , in Hapalocrinus 5 and 

 Stephanocrinus 6 (No. 6, c). The fifth combination (ab — cd — e — ) 

 has not yet been discovered. 



Fig. 5, No. 7, illustrates one of the five possible combinations 

 in which three- and two-basals are anchylosed, as abc — de — , etc. 

 Of these only one is known, abc — de — in Mycocrinus, 1 as figured. 



Fig. 5, No. 8, shows the complete type of anchylosis (abede). 

 While this formula recognizes but one type of complete anchylosis, 



1 Ref. 6, pp. 150, 151. 



2 This combination was found recently, by the writer, in two specimens of Allage- 

 crinus americanus in a large collection of that species made by Professor Weller at 

 Louisiana, Missouri. 



3 Ref. 3, p. 426. 



4 Ref. 6, p. 153. 6 Ref. 19, pp. 212, 351. 



5 Ref. 21, pp. 95-105, Pis. 9, 10. 7 Ref. 28, p. no, PI. 7, Fig. 4. 



