EHODOCRINID^. 255 



ArchSDOCrinUS laCUnOSUS (Billings). 

 Plate X. Fig. 1. 



1857. Olyptocri7ius lacunosus — Billings; Geol. Rep. Canada (Rep. of Progr.), p. 261, also ibid. 1859, 



Decade IV., p. 61, Plate 8, Pigs. 3 a-e. 

 1881. Archceocnnus lacunosus — W. and Sp. ; Revision Palseocr., Part II., p. 190. 



The only known specimen is somewhat crushed^ and its exact form can- 

 not be ascertained, bnt it was probably subglobose. The median line of the 

 rays is followed by ridges, which grow quite prominent upon the distichals, 

 and the surface of the plates is completely covered by small rugose pits and 

 wrinkles. 



Infrabasals very minute, not visible from a side view. Basals unusually 

 large, the largest plates of the calyx ; their truncated upper side very wide. 

 Kadials slightly smaller than the basals, the two facing the posterior side hep- 

 tagonal, the others pentagonal, all sharply angular below. Costals rather 

 small. The three lower distichals take part in the calyx ; they are small 

 and curved like free arm plates. Arms ten at their origin, rounded, rather 

 delicate, bifurcating once or oftener, the branches divergent, and composed 

 of short interlocking pieces. Interbrachials large ; those between the radials, 

 which are almost as large as the basals, rise to the middle of the second 

 distichals, and are followed by two plates in the second range, and others 

 above • anal side wider, plates arranged : 1, 3, 4, etc. Column round, tap- 

 ering considerably downward ; the nodal joints very high, even those next 

 the calyx, which are twice as wide as the intervening ones, and thick and 

 rounded at the edges; the internodal joints comparatively short. At six cm. 

 from the calyx the internodes contain five joints, and this number apparently 

 does not increase in the lower part of the stem. 



Horizon and Locality. — Upper part of Trenton group ; Ottawa, Canada. 



Tyjpe in the Canada Survey Museum at Ottawa. 



ArchsBocrinus pyriformis Billings. 

 Plate X. Figs. 3a, h. 



1857. Thysanocrinus {Modocrinus) pyriformis — '^. Billings ; Geol. Rep. Canada (Rep. of Progr.), p. 263. 

 1859. Rhodocrinus pyriformis — E. Billings; ibid., Decade IV., p. 61, Plate 6, Pigs. la-d. 

 1881. Archceocrinus 'pyriformis — W. and Sp. ; Revision Palseocr., Part II., p. 190. 



A large species. Calyx obconical or pyriform ; one fourth higher than 

 wide; greatest width across the second distichals, slightly contracting above. 



