Vol. 54.] 



ME. F. A. BATHER ON PETAL0CRINF8. 



401 



30. Petalocrinus, Welter Sf Davidson. By F. A. Bather, Esq., 

 M.A., F.G.S. (Read April 20tli, 1898.) 



[Plates XXV & XXVI.] 



Contents. 



Page 



I. History of the Genus 401 



II. Greological Relations of Petalocrmus 402 



III. Description of Material 403 



IV. Anatomical Description of the Genus 407 



V. Systematic Description of Genus an d Species 420 



VI. The Affinities oi Petalocrinus 436 



VII. Summary 439 



I. History oe the Genus. 



Among the geological collections from Gotland, preserved in the 

 Riksmuseum at Stockholm, there have long been some curious fan- 

 like objects, obviously echinodermal, but beyond that of doubtful 

 significance. Study of these in September 1890 led to the con- 

 clusion that they were crinoidal ; not cup-plates, however, as some 

 had supposed, but dichotomous arms in each of which the branches 

 were fused together, forming what may be termed an ' arm-fan.' 

 Although it seemed probable 



that they were of Inadunate -ri- i -n > i • • vi- 



^ ... •^,, , . ,, -cig. 1. — retalocrinus mirabihs, 



amnities, they were not, m the „...„-^ ^ a x z- 



, r • -J specimen g. Arm-fans arbi- 



absence oi more precise evidence, -ttr.^n z. j • / n 



described in Part I of 'The trarzltj numbered i-y. (Drawn 



described m ^art 1 o± iiie ^ j^^^ ^^ ^^ ^^^^^ . ^ ^ 



Crinoidea oi Gotland (Kongl. 't.^/^. t. j ? . 



Sv. Yet.-Akad. Handl. vol. XXV, P^oyraj^h and a plaster 



No. 2, Dec. 1893). Fortunately, ^ 



about this timeMrs. A. D. David- 

 son, now of Whiting (Ind.), dis- xM^S^^H^h-^ 

 covered in the contemporaneous f^^'i?^^^^^^^^ 

 rocks of Iowa similar fossils, ^^!^^^ ^ "^^^^ '^ 

 two of which retained the •• ^^^^^^SftW.^-^ ^^S' 

 five arm-fans in their natural 'f^^^^^w^^?=^^gP^ 

 position, like the petals of a *^^^^P^M^^^!i^^ 

 dog-rose around a small calyx ^^^^^i^m^^^^M 

 (text - fig. 1). These were ^X^wr^^^^li 

 shown to me by Mrs. Davidson 

 on her visit to England in the ^ 

 summer of 1891, and proved [Nat. size.] 

 the correctness of my surmise 



concerning the Gotland fossils. The Iowa specimens, however, 

 were taken back to America, and subsequently submitted by their 

 owner to the Assistant in Palaeontologic Geology at the Unive: sity 

 of Chicago, Mr. Stuart Weller, who prepared a paper entitled 

 ' Petalocrinus mirabilis (n. sp.) and a New American Fauna.' ^ 



^ Journ. of Geol. vol. iv (1896) pp. 166-173 . 



2f2 



