KONGL. SV. VET. AKADEMIENS HANDLINGAli. BAND 25. N:U 2. 155 



Gissocrinus typus, n. sp. 

 (Plate VIII, figs. 261—283). 



1878 G. arthriticits, Angelin (non Phillips) pars, Iconographia, p. 10, Tab. 111, fig. 3 and fig. 2 pars> 



figs. 1 and 5 6?, Tab. XXIX, fig. 75. 

 1878 Gr. punctuosus, Angelin pars, Iconographia p. 10, Tab. XXVII, fig. 1 injirna pars, fig. 1 a, 1 b, 



le, fig. I dl, Tab. XXIX, figs. 73, 73 </, 75 d, 76 and 76 a. 

 1878 G. nudus, Angelin? Iconographia, p. 10, Tab. XX, fig. 20. 

 1878 G. tubulatus, Angelin? Iconographia, p. 11, Tab. III. fig. 4. 



Diagnosis. 



Diameter of closed crown greatest at level of IVBr. Dorsal cup a fairly regular 

 cohe; its plates marked with radiating ribs formed by the concrescence of granules. IBB 

 verv low. BB greatest width equal to height. RR slightly wider than high. IBr 1. 

 IIBr 1. Arms branch from 4 to G times. Arm-ossicles very variable in shape, but expand 

 into a distal ridge, and are slightlv cömpressed laterally. Covering-plates about 5 to the 

 ossicle. Ventral sac vertical, distally composed of parallel series of almost quadrangular 

 plates, lying nearly side by side, with regular transverse folding. Stem-ossicles circular, 

 low, of equal height, but alternately ridged; lumen small. 



This species is by far the most common of the Gotland Gissocrini, and there are 

 in the Riksmuseum sonie thirty specimens that can with certainty be referred to it. It 

 answers in the main, though by do means entirely, to the G. arthriticus of Angelin ; and 

 since this was the species taken by Angelin as the type of the genus, I retain it as sueh 

 under the liame G. typus. As is well known it is by no means always the case that the 

 arbitrarv type coincides with the natural type, that is with the most normal species of 

 the genus, and wc may reasonably doubt the perfect vvisdom of a rnle that sometimes 

 elevates as the type-species a form that is obviously aberrant. Fortunately, so lar as the 

 Gissocrini from the bed f of Gotland are concerned, the present species may be legitim- 

 ately considered as the natural type; not only is it the most prolific in individuals, but 

 it forms a centre around which the other species may be grouped according as they vary 

 from it in this or that direction. 



The specimens from Follingbo were öiostly known to Angelin and probably include 

 the originals of all the figures mentioned above. It has not, however, been possible to 

 identify all of these, owing to the fact that the figures are largely restored and that raany 

 of them are composed from more than one specimen. I also refer to this species a fine 

 large sj)ecimen from a quarry between Bara and Wallstena. Like all specimens from this 

 locality it is well-grown, but in other respects presents nothing worthy of comment. It 

 will be alluded to as w. 



Description. 



In the fossil specimens with the arms closed around the ventral tube the diameter 

 of the crown is greatest at about the level of IVBr; it contracts by about 2 mm. at the 

 level of YIBr, and then expands again slightly. 





