ICHTHYOCRINIDAE 277 



visible as a mere point. The radials and radianal all come down to the stem and rest upon it. 

 The infrabasals have completely disappeared, and in the place they once occupied there is 

 now only an open space, larger than the lumen of the stem, but representing the axial canal 

 of the calyx where it opens out into the chambered organ. The large size of this opening 

 negatives the idea that the loss of the IBB was due to their adhering to, or fusing with, the 

 stem, as in Forbesiocrinus and some other genera of this group. If it were so, the axial canal 

 should remain of the normal size. 



The space thus left by the disappearance of the infrabasals is of course radial in posi- 

 tion, as they were, and it coincides with the usual orientation of the stem canal in pseudo- 

 monocyclic or crypto-dicyclic crinoids such as Isocrinits. A similar condition occurs in 

 Cleistocrinus, Euryocrinns and Amphicrinus, where the IBB are also wholly or partially 

 resorbed. 



Among the specimens figured is the one mentioned by Angelin on p. 13 of the Icono- 

 graphia under /. pyriformis as having been deposited by Dr. Linnarsson in the Geological 

 Museum at Stockholm (PL XXXV, figs. i$a-c), which appears at first glance to be a depar- 

 ture from the characteristic form of the species in the direction of /. pyriformis; yet the 

 measurement of dimensions at the upper IIBr gives nearly the average proportion for the 

 species, 1 to 1.5, while the base tells the story exactly (fig. 15c). 



Types. The original of Angelin's pi. 22, figs. 20, 21, must be regarded as the type, and 

 the other Swedish specimens figured herein, except Plate XXXV, figure 15, as cotypes. All 

 are in the Riks Museum at Stockholm. 



Horizon and locality. Silurian, Wenlock Group, horizons d and /; Gotland, Sweden. 



Ichthyocrinus laevis Conrad 

 Plate XXXIII, figs. 1-13 



Ichthyocrinus laevis Conrad, Jour. Acad. Nat. Sci. Philadelphia, VIII, 1842, p. 279, pi. 15, fig. 16. — 

 D'Orbigny, Prodr. Pal. Stratigraphique, I, 1849, p. 46. — Hall, Nat. Hist. New York, Pal. II, 1852, 

 p. 195, pi. 43, figs. 2a-p. — E. Billings, Canadian Nat. and Geol., I, Feb. 1856, p. 59, pi. frontispiece, 

 fig. 4. — Pictet, Traite Paleontologie, IV, 1857, P- 319, pk 100, figs. 170, b. — Beyrich. Monatsber, 

 Akad. Wiss. Berlin, Feb., 1871, p. 45 (Transl. in Ann. and Mag. Nat. Hist., (4) VII, p. 403). — 

 Quenstedt, Petrefaktenkunde Deutschlands, IV, 1876, p. 515; Handbuch Petrefaktenkunde, 1885, 

 p. 947. — Von Zittel, Handb. Pal. 1879, p. 356, fig. 243; Grundziige Palaeontologie, 1895, p. 138, 

 fig. 270; 1910, p. 165, fig. 300. — Miller, N. A. Geol. and Palaeontology, 1889, p. 256, fig. 344. — Zittel- 

 Eastman, Textbook Paleontology, 1896. p. 164, fig. 270; 191 3, p. 204, fig. 305. — Grabau, 1901, p. 159, 

 fig- 54- — Springer, Jour. Geology, XIV, 1906, p. 477, pi. 6, fig. 1. 



Cyathocrinites pyriformis, Hall, Nat. Hist. New York, Geol. Fourth District, 1843, p. in, fig. 3, p. 112, 

 tab. 17, fig. 2. 



Lecanocrimts simplex. Hall, Nat. Hist. New York, 1852, Pal. II, p. 202, pi. 46, figs. 20-e. 



Not Ichthyocrinus laevis, Angelin, Icon. Crin. Sueciae, 1878, p. 13, pi. 22, figs. 20, 21= I. gotlandicus; 

 nor pi. 9, figs. 17, I7a-e = l. pyriformis. 



Type of the genus. 



Species variable, attaining" a large size. Crown elongate pyriform, with 

 truncate base; expanding gradually from base to about the upper IIIBr; height 

 to width at upper IIBr, about i to 1.6; spread of calyx from RR to same level, 

 about 1 to 4. Side outline of calyx concave below, becoming convex upward, 

 cross-section about circular; sometimes with slight projections at the radial 

 ridges. Plates strongly imbricated; surface smooth. Maximum crown, 75 mm. 

 high by 52 mm. wide at upper IIIBr; minimum, 14 by 11 mm.; average width 

 of base, 6.5 mm. 



