98 F. A. BATHER, CRINOIDEA OF GOTLAND. 



height is 4.75 mm.; its upper slopes, which are verv slightly concave, are 4 ram. in 

 length. The secundibrachs förra two arms of equal size, and of the same externa! ap- 

 pearance as the axil-arms of the other radii. The extreme length of the secnndibrach series 

 is 34 mm. The ossicles, except the extreme proximal and distal ones, are of the width 

 of 2.75 rara. throLighout. HBi^ is 4 rara. wide below and 2.75 mm. wide above; its 

 height is 1.9 ram. Succeeding ossicles gradually lessen in height, from l.i rara. to 0.75 

 mm. or less. (Fig. 133). 



Ant. and 1. post. arms. — IBr, seen externally appears almost as a wide reetangle, 

 but is really of very wide lunate shape; the middle portion is almost flat, bnt at either 

 end the plate bends round sharply; the flat portion is bevelled above and below. The 

 plate rests on the large radial and abuts by its corners on the adjacent inferradial. Its 

 width is 8 mm.; its greatest height is 1.2 rara. lax is roughly triangulär; the ends of 

 its base are curved upwards to raeet the sides; its upper slope, 4 mm. long, supports an 

 arm which rests in a square-cut notch; its outer slope, 7 mm. long supports Ilax. The 

 main-axils and arms numbered 9 in the type-specimen, but in one of the Fårö specimens 

 they can be traced up to the llth axil. The main-axils resemble lax in shape, with the 

 addition of an upturned portion; the lower or inter-facet portions curve gently round till 

 they becorae perpendicular to the surface of the anal plates; över these they form the usual 

 arch, which leaves exposed only x and part of the second plate. The axil-arms clo- 

 sely resemble one another and the branches of the 1. ant. arm; they lessen very slightly 

 in width and length as they recede from this, and lie parallel to one another. In each 

 axil-arm the first alphabrach is wider than succeeding ossicles; it rests in a curved facet, 

 and the outer edges of the articulation are slightly bevelled. (Fig. 129). 



As seen from the exteriör when the crown is closed, the branches of the 1. ant. 

 arm and the axil-arms all appear quite simple. A close inspection, however, shows that 

 the sutures between the ossicles are not absolutely parallel, but lie at alternate angles. 

 The slope of the suture is rarely perceptible on the outer curve of the ossicles, but in— 

 creases towards the sides. This having been observed, careful dissection of the type- 

 specimen revealed the fact that as the sutures curved round towards the ventral side they 

 almost, or sometimes quite, met on alternate sides, so that the line formed by them was 

 a zigzag and each ossicle was really triangulär in its dorsal outline. Then also it was 

 seen that each ossicle bore a true pinnule on its outer side. (Figs. 134, 135, 138). 



A section of a specimen from Fårö, at about 18 mm. from the base of the axil- 

 arms, shows the following points — width of arm-ossicles 2.5 mm.; extreme depth dorso- 

 ventrally 3 mm.; depth to bottom of ventral groove 2 mm.; groove large and curved: 

 axial canal distinct, fairly large, and not far removed from groove. (Figs. 139, 140). 



The Pinnules are set closely on both sides of the arm, so that they touch one an- 

 other at their l)ases; in each arm-ossicle the articular face to which the pinnule is attached 

 slopes outward below and projects beyond the preceding ossicle; it has a gentle concave 

 curve. Each pinnule is about 8 ram. long and 6 mm. wide; perhaps longer in the proximal 

 region, and certainly shorter in the distal region. The proximal ossicle of each pinnule 

 is wide at its base, and its lower side is longer than its upper side; thus the pinnule is 

 given an upward direction greater than it would have received from the slope of the 



