2 SMITHSONIAN INSTITUTION 



PLATE A 



Larval Development of Existing Cmnoids 



S3'inbols on this and next two plates: B^ basal; R ^ radial ; IBr ^primibrach ; RA ^ radianal ; 

 iRi^interradial; An = antis; p=:perisome; x = anal (radianal). 



PAGE 



Figs. 1-6. Antedon bifida (Pennant) [rosacciis atictt.] 8o 



Fig. I. Skeleton of Pentacrinoid larva at incipient brachial stage with orals opened ; dried specimen, 

 showing- reticulate structure of the plates, with anal plate x in the zone of radials, 

 resting on posterior basal and encroaching upon side of right posterior radial. (After 

 W. B. Carpenter, pi. 41, fig. I.) X 30. 



2. Pentacrinoid larva at later stage, with centrodorsal and cirri well developed, almost ready 



to cast off the stem. Anal x detached from the radials (which are nearly closed 

 beneath it), and lifted from beneath them by the growth of the anal tube a, to which 

 it is attached. See note on p. 81. (After W. B. Carpenter, pi. 40, fig. 2.) X 30. 



3. Opposite view of same specimen, with one ray removed to show the oral apparatus; orals, 



0, 0, now completely separated from radials, and relatively carried inward by the 

 development of the membraneous perisome, />. (After W. B. Carpenter, pi. 40, fig. i.) 

 X30. 



4. Skeleton of Pentacrinoid larva at stage with ventral side closed by the folding together of 



the orals, 0, 0: cirri just beginning to appear. (After W. B. Carpenter, pi. 39, fig. i.) 



X3S. 



5. Early Pentacrinoid larva, spirit specimen, with orals opened but with tentacular apparatus 



retracted, showing basals, radials and rudimentary primibrachs ; cirri not yet devel- 

 oped. (After W. B. Carpenter, pi. 39, fig. lA.) X IS- 



6. Similar specimen at somewhat later stage than the last ; showing incipient development of 



arms from the IBr, and the relative increase in size of radials. (After W. B. Car- 

 penter, pi. 39, fig. IB.) X IS- 



7. H3T30thetical figure of primitive Flexibilia calyx ; with infrabasals, radianal, anal x between 



radials, and two primibrachs — for comparison with figures on this and two succeed- 

 ing plates. (From author's paper of 1906, Jour. Geology, XIV, pi. S, fig. 9.) 



Fig. 8. Holopus rangii d'Orbigny 82 



Fig. 8. View of the disk with closed orals, 0, 0, perforated ; small plates at base of arms separate 

 the orals from the radials. (After P. H. Carpenter, Challenger Rep. St. Crin., pi. 3, 

 fig. 2.) Xf. 



Fig. g. Thaumatocrinus renovatus P. H. Carpenter 83 



Figs. 9a, b. View of the disk from above ; showing the pyramid of closed orals, marginal zone of 

 small plates between orals and interradials, and the anal tube with its appendage of 

 strong plates ; the protuberances seen between the arm-bases are the interradials which 

 separate the radials all around. (After P. H. Carpenter, Phil. Trans. Roy. Soc, 1883, 

 pi. 71, fig. S-) X IS- 



Figs. lo-iS- Promachocrimis kerguelensis P. H. Carpenter 84 



(Larval stages ; to be consulted after the figures on Plates B, C) 

 Fig. 10. Prebrachial stage. Calyx composed almost exclusively of basals and orals ; minute radials 

 have appeared, that of the right posterior ray being smaller than the others; the 

 radianal is larger than the radials, having evidently preceded them, and has passed 

 from its primitive position toward the left of r. post. R. X 44- 



11. Slightly later stage. Radials are now as large as the radianal, which retains about the same 



position as in the last figure. X 45- 



12. Early brachial stage. Radials much larger than radianal, which is still in the same zone 



as they are, indenting the left margin of r. post. R ; two brachials, the primibrachs, 

 have developed. X 45- 



13. Later stage, showing further increase of radial and brachial parts. X 35- 



14. Much later stage, in which radials and brachials have further increased in size, and inter- 



radials having to some extent the functions of radials have appeared between the 

 regular radials. RA has passed upward beyond the plates of the dorsal side. X 35. 



15. Outline drawing showing the points of distinct IBB, which are frequently invisible. X 22. 



Recent. Collection German South Polar Expedition, steamer Gauss. Near Kerguel 

 Islands, Antarctic. 



