KONGL. SV. VKT. AKADEMIENS HANDLINGAR. BAND 25. N:0 2. 129 



Key to the Gotland species of Cyathocrinus. 



A. -Stem-ossicles rather low and alternately ridged. 



I. Stena of moderate width; 

 Cup more or less conical. 



a. Cup with straight sides. 



a. Plates plane; granular C. Diance. 



b. Plates axially folded and striate C. striolatus, 



b. Cup with convexo-concave sides, irregular. 



c. Plates plane; sraooth or pustulate C. visbycensis. 



<l. Plates tumid; sraooth C. acinotubus. 



II. Stem rather fine; 



Cup expanding suddenly and greatly in raiddle of radials. 



(The three species exemplify thé latter character in different degrees.) 



a. I Bi*! wedge-shaped. 



e. Radial-facet almost vertieal; 



arm-ossicles low, rather wide... C. glaber. 



I». IBr, not wedge-shaped. 



f. Radial-facet gently sloping; 



Arm-ossicles long, fine C. muticus. 



</. Radial-facet vertieal; 



Arm-ossicles low, verv wide C. distensus. 



B. Stem-ossicles verv low and equal. 



III. Stem verv wide; 



Cup with convex sides. 



h. All plates high; alightly tumid; 



Covering-plates .'V ., — 4 to an ossicle.. C. longimanus. 



i. All plates low, plane; 



Covering-plates 1 — 1 ' A. to an ossicle... C. ramosus. 



This key does not represent the affinities of the species. They may perhaps be 

 shown as follows: 



C. ramosus C. longimanus C. distensus 



C. muticus. 



i 



C. acinotubus C. glaber 



C. Diano?, ___________ — 



C. visbycensis C. striolatus 



This seheme is in accordance with the facts of geological distribution; hut it must 

 not be taken as representing a genealogical tree. 



K. Sv. Vet. Akad. Handl. Rand. 25. N:o 2. 17 



