1879.] NATURAL SCIENCES OF PHILADELPHIA. 377 



EXPLANATION OF PLATE 15. 



Letters referring to all figures on this plate : u = underbasals ; b = ba- 

 sals ; ? = radials; r} = primary radials ; r 2 = secondary radials ; r 3 = ter- 

 tiary radials; > = patelloid plates; a = arm plates; ' = interradials ; d = 

 axillary plates ; an = anal plates ; br == brachial plates ; A = anterior side ; 

 P = posterior side. 



Fig. 1. Diagram of Forbesiocrinus, showing the fundamental arrangement 

 of plates in the Ichthyocrinidge. 



Fig. 2. Diagram of Taxocrinus, showing, in connection with Fig. 1, the 

 distinction in the anal side between this genus and Forbesiocrinus. 



Fig. 3. Diagram of Barycrinus, showing the fundamental arrangement of 

 plates in the Cyathocrinidse. 



Fig. 4. Apical plates in Actinocrinus. 



Fig. 5. Apical plates in Platycrinus. 



EXPLANATION OF PLATE 16. 



Fig. 1. Diagram of Anomalociinus. 



Fig. 2. Diagram of Heterocrinus. 



Fig. 3. Diagram of Iocrinus. 



This and the following figures on this plate are given to show the 

 development of the anal plates from one genus to another. 



Fig. 4. Diagram of Hybocrinus. 



Fig. 5. Diagram of Dendrocrinus. 



Fig. 6. Diagram of Homocrinus. 



Fig. 7. Diagram of Poter iocrinus. 



Fig. 8. Diagram of Cyathocrinus. 



EXPLANATION OF PLATE 17. 



Fig. 1. Pentacrinoid larva of Antedon rosacea. (After Airman.) s = stem; 

 cd = centrodorsal plate ; b = basals ; r = radials ; or = oral plates. 



Fig. 2. Ventral side of Cyathocrinus, showing the oral plates, the apical 

 and radial dome plates being removed. 

 d 



or 



= oral plates equivalent to d in Fig. 4. 



Fig. 3. Ventral side of Cupressocrinus, showing the hydrospires; h = con- 

 solidating apparatus of European authors; g = openings which, from 

 25 



