DESCRIPTION OF PLATES XLV— XLVIII. 



(Lister. Astrosclera.) 



REFERENCES. 



c. canal. <•'. small canal. 



c. ch. ciliated chamber. 



c.j. scattered cells of the jelly. 



cort. cortical layer of the skeleton. 



/. c. large cells of the soft tissue. 



in. surface membrane. 



p. pore. 



sk. skeleton. 



sk. e. skeletal element. 



spli. spherule, young stage of skeletal element. 



spic. spicule (of foreign origin). 



All the Figures ichich Jolhno are draicii from specimens Jroin Lifxi. 



Plate XLV. 



Fifi. L Side view of a specimen S mm. in height. 



Fk;. Ire. View of the upper surface of the same specimen. 



Fig. '1. Side view of a specimen which has curved in the course of growth, so that 

 its axis comes to be parallel with the surface of attachment. Height 10 5 mm. 



Fig. 2«. View of the upper surface of the same specimen. 



Fig. 3. Part of a chip broken from the skeleton, x 570. 



Fig. 4. Four skeletal elements, from a thin section, x 690. 



Fig. 5. Skeletal elements from the upper surface in difl'erent stages of growth, x 690. 

 rt. One of the skeletogeuous cells of the jelly, containing a small spherule 8/j. in 



diameter. Other cells of the jelly are also seen. 

 6 — (/. Growing spherules, invested by the skeletogenous cells, n. Nuclei of the latter. 

 e. A growing spherule still free in the jelly. 



f. Spherules becoming adherent and with flattened adjacent surfaces. 

 (J. A skeletal element in the spheraster stage. 



Fig. 6. Section of the organic basis of the skeleton of a decalcified .specimen. x 570. 

 At b a skeletal element with an unusually large centre is shown. 



Fig. 7. Two of the depressions in the upper surface (represented in Figs. Ire and 2a) 

 seen from above and illuminated by direct sunlight, b. is seen obliquely. The surface mem- 

 brane is shown perforated by pores (p.) and containing spherules. 



