184 SMITHSONIAN INSTITUTION 



IBB large, visible as pentagons in side view. BB usually higher than RR. 

 RA quadrangular. Anal x wide, truncate above. Radial facets moderately 

 wide (to width of R as 1 to 1.8) leaving sloping shoulders for the iBr areas. 

 IBr usually 2; IIBr few, usually 2 or 3. Arms round, fairly thick. Column 

 unknown, but must have been quite large. 



The elevated ridges or costae were made by Angelin the principal character both of the 

 genus and species. As compared with other species in which they occur this is usually 

 peculiar in having a horizontal ridge passing from one radial to another (the radial com- 

 missure). It is interesting to note that in one Gotland specimen not from the same locality as 

 the others (PL XI, figs, ga, b) the transverse ridge is wanting, and also the depressed areas at 

 the juncture of the suture lines — the specimen in these respects as well as in the general 

 appearance resembling those from Tennessee. The specimen showing the principal arm 

 structure (fig. 7) is much larger than the others, but it is otherwise characteristic. 



Angelin's P . costatus was probably a young individual of this species, with a higher 

 calyx and more numerous costae. The figure is shown to be about two and one-half times 

 enlarged, but the specimen cannot be found. 



Types. Those of Angelin's figures and the others figured herein are in the Riks Museum. 

 Of Angelin's there is only the original of his plate 15, figure 10 — his other figure being a 

 restoration. 



Horizon and locality. Silurian, Wenlock Group, horizon /; mostly from Klintberg and 

 Lau, some from Wisby — and perhaps from horizon d at the last locality — Island of Gotland. 



Pycnosaccus nodulosus Angelin 

 Plate XI, figs. 11-16 



Pycnosaccus nodulosus Angelin, Icon. Crin. Sueciae, 187S, p. 14, pi. 15, figs. 12, 14; pi. 28, fig. 2g. — - 

 Wachs'muth and Springer, Revision Palaeocrinoidea, pt. I, 1879, p. 41. — Bather, Ann. and Mag. 

 Nat. Hist, (6)V, 1800, p. 387. 



A very small species, having little to distinguish it from the preceding ex- 

 cept the greater height of RR and width of the radial facet, and the fact that the 

 anal plate is acuminate instead of truncate. The proportionate height of IBB 

 to BB to RR is 1:5:6; width of radial facet to the width of radial is about as 

 1 to 1.2, the result being that the interbrachial spaces are very narrow. The 

 irregularity in the number of IBr, and the tendency to take on a second one by 

 the intercalation of a very thin or short rudimentary plate beneath the axillary 

 (PI. XI, fig. 11a), has been mentioned in the generic discussion. The costae, 

 while obscure, are plainly in evidence. Angelin gave as the only specific char- 

 acter that the arms are nodulose, but specimens as now prepared and figured 

 show nothing of this beyond the mere convexity of small arm plates. The 

 column, not known in P. scrobiculatits, is well preserved in this species; it is 

 large, composed of wide rounded columnals regularly alternating with narrow 

 ones, without any taper near the calyx. 



