ECHINODEBMA. 



PLATf] I. 



Fio. 1. Aurimlaria antardira viewed from tlie ventral aspect, Magnification L'J diameters, coe., the 



spherical eoelomic vesicle. 



Fin. 2. Some of the calcareous wheels of .1. (i/t/t<ri-/irit. Magnification :.'dd diaiin.-ters. n., seen from the 

 convex side, //., r., and iL, from the concave side. 



FlG. 3. One of the youngest of the llolotlmrioids in the collection, viewed from the side. Magnification 



(in diameter.--. 



FIG. 4. A young Cucumarian, presumably ('. ln-tm, .Indeed at Plymouth in 1905. Magnification 



110 diameters. A key is given to this plate. 



PLATE II. 



FIG. 5. A median longitudinal section through one of the youngest Tlolothurioids in the collection. 

 Magnification aliont lid diameters. The intestine is seen to be perfectly straight and very short, and 

 the stone canal (st. c.) opens into a closed vesicle (a.r.). 



FIG. C. A somewhat lateral longitudinal section through an older specimen than that represented in 

 Fig. 5. Magnification 75 diameters. The axial sinus is seen to communicate with the cojlom by 

 a canal (mad.}. 



Fin. 7. A median longitudinal section through a specimen about the same age as that represented in 

 Fig. (i. Magnification 75 diameters. pitl.,n diverticulnm of the thin-walled rectum, which is in all 

 probability the rudiment of the pulmonary trees. 



FIG. 8, a., l>,, and c. Three transverse sections through one of the younger specimens. Magnification 

 7."> diameters. 8. is through the tentacles; */*. through the middle region of the body, and 

 Si 1 , through the posterior end ; ij. .' curiously deeply-staining packets of cells resembling rudimentary 

 gollads. 



The restriction of the tube-feet to the three ventral interradii is seen, as also the fact that 

 the most terminal tube-feet belong to the uiid-veiitral radius. 



