MONOGRAPH OF THE EXISTING CRINOIDS. 191 



Promachocrinus and Thaumatocrinus. 



The calyx of the pentacrinoid larva of Promachocrinus is very robust, more so 

 than that of any other comatulid, and is characterized by pronouncedly convex 



V^r 1- LATERAL VIEW OF A YOUNG SPECmEN Or PENTAMETROCBINUS, SP. FROM ICELAND. SHOWING THE RELAT.ONSH.rS OF 

 FIG. '^-^'^'^^^IZoZsj^. BASA.^, RATALS, ASH ,STERRAD.A,^. AND THE PEK.SOM.C PLATE3 OF THE »,3K. 



Sides and great breadth across the radials. This is probabb" due to a more than 

 usually rapid growth of the internal organs, intensified by a duninut.on in the rapid- 

 ity of the growth of the calyx plates resulting from the coldness of its habitat. 



