MUSEUM OF COMPAEATIVE ZOOLOGY. 145 



the water-tubes described in other Echinoderms is likewise found in 

 Echinarachnius. 



5. The first-formed calcareous deposits of the test in the young Echin- 

 arachnius are trifid in shape, varying in number in different specimens. 

 The extremity of each trifid division later in its growth bifurcates, and 

 the calcareous body thus formed appears to be enclosed in a transparent 

 wall, which has a spherical outline. 



6. Spines are very early formed, and are proportionally very large as 

 compared with those of the adult, as in other Echinoderms. 



Cambbidgb, March, 1886. 



VOL. XII. — NO. 4. 10 



