KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAN 



D 25. 



n:o 



127 



MUTH and Spbingbe (loc. c/t.) inay be considerably reduced. Auiong species described 

 from the Silurian of North America I can only tind three that can claim to be considered 

 members of this genus, viz., C. cora, Hall, C. waukoma, Hall and C. van Hornei, S. A. 

 Miller. The axial folding on the cup-plates of the two former sufficiently distinguishes 

 them from all the Gotland species, in which the plates are either smooth or verv slightly 



Text-fig. 18. Morphology of Cyathocrinus. 



1. The dissected cup; with the anterior radius on the right. 



2. Longitndinal median seotion through ten colnmnals of V. adnotubus. s, stereom of ossicle; m matrix filling 



axial canal; c, ealcite taking the j)!ace of former ligaraent. 

 ?>. Transverse section through the stem of C. adnotubus. Letteting as above. X 5 diam. 



4. Transverse section through a brachiaJ (TIIBr) of C. adnotubus. Br. body of the ossicle; a.r., axial canal; 



'-/.. vential groove; cp., covering plates. X 8 diam. 



5. A youag iudividual of C. adnotubus (':). The extreme length of soine of the brachials mav be only apparent 



and dne to the difiicnlty of seeing the sutures; it is, however, noticeable in the young of other 

 genera. Nat. size. 

 b a. A firat primibach of the same, showing that the axial canal is not vet separated from the ventral groove; 

 X 3 diam. 



6. Ventral surface of the calvx of C. planus with ambulaerals and interambulacrals removed. A, deltoids, and 



M. madreporite; these surround the peristome, and on their edges are seen iudentations for the 

 reception of the ambulaerals: x. anal. From E 6007, B.M.; X 2 diam. 



7. Ventral surface of the calyx of C. mammillaris, Piiill., with tegmen complete. A, deltoids, in great part 



covered by ia, interambulacrals; cp, eovering-plates. which are irregular; r, anal, which is partly 

 broken. E 288 B.M.; X 2 diam. 



striated or concentrically ridged, and even suggests the possibility that they may belong 

 to some other genus; while the very peculiar shape of C. van Hornei, if not confined to 

 the only known specimen, would distinguish it from every other species of this genus 

 vet known. 



