KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 25. N:0 2. 97 



Basals 3 observed. Left basal enters stem-facet and occupies almost the whole width 

 of the hinge; its width is 10.5 mm., its height 4 mm. 



Stem-facet at the extreme apex of the basal triangle; since the stem is attached, the 

 relations of the basals to it are not quite clear. 



Radials: All the sutures are very obscure. L. ant. R, — the two halves are not 

 separated: the inferradial occupies the whole of the hinge-line and rapidly narrows above; 

 all its sides are concave; its height is 4 mm., its width below 10.75 mm., its width half- 

 way up 6 mm., its width above 4 mm.: the superradial is the segment of a circle with 

 a square-cut facet for the arm; its width above is 7 mm. while the width of the facet is 

 (j mm.; its height is 2.75 mm. 



Large radials: it is verv difficult to distinguish the sutures between them and the 

 r. post. and r. ant. inferradials; they appear to be bounded as follows, — (1) articular 

 facet, 7.25 mm.; (2) radianal, 2 ram.: (3) post. B, 4 mm.; (4) 1. ant. inferradial, a con- 

 vex curve, <J mm.; (5) 1. ant. super-radial, a concave curve, 4 mm.: the extreme height 

 is 8 mm. 



Radianal is a very small 4-sided plate, bounded as follows, — (1) 1. post. R, 2 mm.; 

 (2) IBi-j and Ilax, 2.5 mm.; (3) T-piece, 2.5 mm.; post. B, 1.1 mm. 



T-piece is apparently about 8.75 mm. wide above and 6 mm. wide below. Above 

 it is bounded by a shallow concave curve; below it appears to have been considerably 

 excavated for the reception of the stem. Its sides abut on the r. post. and r. ant. infer- 

 radials. Its upper corners may touch some of the main-axils. 



Anal struetures: x rests on the T-piece; it is gently curved, with a slightly 

 concave suture below, with sides apparently straight, and with a markedly concave suture 

 above. Its width is about 8 ram.; its height at the sides 2.75 mm.; its height in the 

 middle 2 rara. (Fig. 131). 



The plate succeeding x has a convex lower suture but a nearly straight upper one, 

 so that the plate is somewhat lunate; its width is S mm.; its height in the middle 2.25 

 ram. This we may call the 2nd anal plate. 



The next or 3rd plate has its upper and lower sutures almost parallel to one an- 

 other. It is 7 rara. wide, and 2 rara. high. 



The following plates froni the 4th to the 15th graduallv decrease in width, but all 

 have a height of about 2.25 mm., rather less in the last three or four; their upper sutures 

 are fairly straight and parallel, but their sides are irregular owing to the abutment of 

 small irregular plates; thus the shape of plates 4 to 15 is niore or less hexagonal. The 

 width of plate 7 is 4 ram.; of plate L5 is about 2 rara. The small plates that abut on 

 these, and close the tube över (ra its ventral side, are extremely irregular in sizc and 

 shape; they appear to have been fairly solid. 



The tube, which below must have been at least 10 inni. wide, contracts above, 

 where it emerges from the closed arms, to a tube of 2 rara. diameter with a lumen of 

 0.5 mm. diameter. (Fig. 132). 



Arms: L. ant. is two-branehed. IBr, is axillary; it rests in a square-cut socket of 

 the 1. ant. superradial; it is pentagonal; its lower sides slope inwards slightly; its surface, 

 which below is almost straight, becomes rounded above; its width below is 7 mm.; its 



K. Sv. Vet. Akad. Hanill. Band 25. N:o 2. 13 



