DISCOVERY OF THE DISK OF ONYCHOCRINUS 521 



development of arms from the IBr, and the relative increase in size of radials; cirri 

 not yet developed. (W. B. Carpenter, Plate XXXIX, Fig. iB. X15.) 



Fig. 3. — Skeleton of early Pentacrinoid larva at a little later stage, dried speci- 

 men; showing the manner in vs^hich the calyx can be, at that stage, completely closed 

 by the folding together of the orals, o, o; cirri beginning to appear. (W. B. Carpen- 

 ter Plate XXXIX, Fig. 2. X35.) 



Fig. 4. — Skeleton of Pentacrinoid larva, same stage as Fig. 2, dried specimen; 

 showing anal plate x between two radials, and resting on the posterior basal. (W. 

 B. Carpenter, Plate XLI, Fig. I. X30.) 



Fig. 5. — Skeleton of Pentacrinoid larva, in still later stage; showing the anal 

 plate X now being hfted up from between the radials; cirri well started. (W. B. 

 Carpenter, Plate XXXIX, Fig. 3. X25.) 



Fig. 6. — Pentacrinoid larva at a still later stage, when almost ready to cast off 

 the stem. The anal plate x detached from the radials (which are nearly closed be- 

 neath it), and lifted from between them by the development of the anal tube a, to 

 which it is attached; centrodorsal and cirri well developed. (W. B. Carpenter, Plate 

 XL, Fig. 2. X30.) 



Fig. 7. — Opposite view of the same specimen, with one ray removed to show 

 the oral apparatus. The orals, o, 0, now completely separated from the radials, and 

 relatively carried inward by the development of the membranous perisome, p. (W. 

 B. Carpenter, Plate XL, Fig. i. X30.) 



HOLOPUS RANGEI 



Fig. 8. — View of the disk, with closed orals, 0, o, perforated; and small plates 

 at base separating the orals from the radials. (From P. H. Carpenter, Chall. Rep. St. 

 Or., Plate III, Fig. 2. X|.) 



Fig. 9. — Hypothetical figure of primitive Flexibilia calyx; with infrabasals, 

 radianal, anal x between radials, and two primibrachs. 



EXPLANATION OF PLATE VI 

 (On this and the following plate the radianal is shaded with vertical lines.) 



IcHTHYOCRiNUS Conrad 



Fig. I. — /. laevis Corir. Upper Silurian, Grimsby, Canada. 



Fig. 2. — /. suhangularis Hall. Upper Silurian, Waldron, Ind. 



Fig. 3. — /. pyriformis. Upper Silurian, Dudley, England, 



Fig. 4. — /. pyriformis (fide Angelin). X2. Upper Silurian, Gotland, Sweden. 

 From original to Angelin's XXII, 22. 



Fig. 5. — /. intermedius Ang. X2. Upper Silurian, Gotland, Sweden. 



Fig. 6. — /. gotlandicics W. and Sp. X2. Upper Silurian, Gotland, Sweden. 



These figures all show the extra plate — radianal — at the base of the right posterior 

 ray. 



Clidochirus Angelin 



Fig. 7. — C. pyriun Ang. Upper Silurian, Gotland, Sweden. View from right 

 posterior radius. 



Fig. 8. — View from posterior interradius of another specimen — the original to 

 AngeHn, XVII, 6. 



