KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 25. NCO 2. 131 



abnorma! specimens of which he applied theni. In adopting this way out of the difficulty 

 it is as well to state that I have the approval of Professor Lindström. 



Owing to the extreme variability of this species it is almost impossible to draw 

 up a diagnosis that shall enable any ehance specimen to be referred to it, and one must 

 rely largely on characters that are not often to be seen. 



Diagnosis. 



Dorsal cup below radials with regular steep sides, but some or all RK usually 

 spread out at a wide angle. Facet about 2 / 3 width of R; ventral groove deep, narrow; 

 axial canal separate, half-way betwen bottom of groove aud outer edge of facet; fulcral 

 ridge slopes outwards on either side of axial canal. x supports 3 plates. Ventral tube 

 composed of 9 longitudinal rows of hexagonal plates alternating and not folded. Stem 

 round with quinquelobate lumen. Plates of cup smooth or granulate, espeeially round 

 borders. 



Description. 



The Dorsal cup below the radials forms a fairly regular cone with steeply sloping 

 sides; but some or all of the radials, as a rule, spread out at a rather wide angle. The 

 proportional height of the cup varies very much; in the following the numerator represents 

 the height in millimetres, the denominator the width: T 7 T , \\, \%, \l, {$. The cup is lower 

 in proportion as the radials are bent outwards, and is often higher on one side than 

 on the otlier. 



IBB 5, pentagonal, rise up in a line with the stem. Thev varv considerably in 

 height, even in the same individual, but the usual measurements are: height 2 mm. and 

 width 4 mm. Their shape also may be distorted. In one specimen from Snäckgärdet 

 they are swollen and rugose, and partly cover the top stem-ossicle. 



BB 5; 4 are hexagonal and 1 heptagonal. They are about as high as wide, say 5 

 min.; but tliere is considerable variation even in the same individual, thus one basal is 

 2.3 mm. high and 5 mm. wide, while another is o mm. high and 3.7 inni. wide. 



RK 5, very variable. Some continue the line of the cup from the infrabasals up, and 

 their articular facet is directed upwards. < >thers spread out almost horizontally from the 

 cup, and their articular facet becomes parallel with the sides of the infrabasals and basals 

 se that it is actually directed downwards. The edge of the facet is often raised in a 

 little rim. The width of the facet may be taken as 8 /s *bat of the radial; but it varies, 

 and is often increased by weathering. It is horseshoe-shaped, soinetimes long, sometinics 

 broad. The ventral groove forms a sharply incised angle. The axial canal lies half- 

 way between the bottom of the groove and the outer edge of the facet. Just ;it the lower 

 edge of the axial canal is a transverse ridge; or rather, the surface of the facet outside 

 this point is slightly excavated, and the excavation is bounded by two lines that descend 

 gently from the lower part of the axial canal. There are also slight lateral depressions on 

 the inner side of these lines. The space between the inner and outer depressions is 

 slightly granular. Traces of the connection between the axial canal and the ventral groove 

 are to be distinguished m some specimens (tig. 200). 



