KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND. 



25. 



n: 



O 2. 



29 



The Base does not, in most cases, form sx regular equilateral triangle as described 

 by de Koninck. Sometimes the basals spread ont horizontally from the stem and eurve 

 upwards gently (Pl. I, figs. 4, 5); sometimes they bend upwards at a sharp angle (Pl. I, 

 figs. 2, 6). The top of the stem is in the conical form often received within a little rim 

 (Pl. I, fig. 6), bnt this may be absent and the ciip truncated by a smootb plane (Pl. I, 

 hg. 7): in globose forms tliere is a slight eöncavitöy for the stem, hut no rim (Pl. I, hg. 5). 

 BB 5. In the more conical and ovoid forms, when viewed from the outside and counting 

 the suture with the stem as a side, post. B, 1. post. B and r. ant. B are pentagomal, and 

 the last is smaller than the other two; r. post. 1> and 1. ant. B are quadrangular and usually 

 wider than high: the upper sloping sides of the pentagonäl basals make an obtuse but very 

 variable angle with the truncate tops of the quadrangular basals (Pl. I, fig. 1). In the 

 more globular forms the essential shape of the basals is the same, but, owing to the ab- 

 sence of a sharp bend at the junction with the stem, the appearance is different: in these 

 also the angle formed by the upper sides of the pentagonal with those of the quadrangular 

 basals is so wide as to be almost a straight line: consequently the outline of the whole 

 base forms an almost regular triangle. The basals vary eonsiderably both in si/.e and 

 proportion, as shown by the following measurements: in these the first eolumn gives the 

 absolute height in inillimetres of 1. post. B, measured from the suture with the stem, or 

 from the corresponding bend in the plate when a rim is present; the second eolumn gives 

 the height in inillimetres of the cup from the same point to the artieular faret of the left 

 anterior radial; the third and fourth columns show the proportion. Specimens a and b 

 are of the ovoid form, the rest are conical or ovoido-conical. 





I. 



11. 



III. 



IV. 



a . . . 



0.75 



3.1 



1.— 



4.13 



b . . . 



0.75 



2.75 



1.— 



3.6 



c . . . 



2.- 



G.25 



1.— 



3.12 



cl . . . 



1.75 



5.4 



1.— 



3.08 



e . . . 



1.4 



3.5 



1.- 



2.5 



f ■ ■ ■ 



1.6 



3.75 



1.— 



2.34 



g . . . 



1.75 



4.— 



1 — 



2.28 



RR 5. If the radial processes be not taken into account, the plates may be described 

 as follows: 1. ant. R triangulär, with its lower sides usuallv curved, equal to one another 

 and generally shorter than the third or faeet side; it does not touch the basals: 1. post. R 

 seven-sided, being l)ounded by 1. ant. R, ant. R, 1. post, B, post. B, R', r. post. R, and facet: 

 r. post. R and r. ant. R four-sided; the side where they meet each other is however some- 

 times very short, or even non-existent, owing to the extension of R'; ant. R eight-sided, 

 being bounded by r. ant, R, R', r. ant, B, 1. ant. B, 1. post, B, 1. ant, R, and facet, The 

 artieular facet (Pl. I, fig. 10) is excavated in the shape of a four-sided pyramid, with the 



