BY T. GRIFFITH TAYLOR. 



57 



shaped area probably represents the under surface of the lancet 

 plate, and its relative position is given in fig. 4. 



Systematic Position. — The character of the ambulacra, which 

 are distinctly linear and narrow, serves to sepai"ate this genus 



Fig. 3. -(Somewhat diagramatic). Portion of ambulacra. The ridges (G) 

 between the side-plates, and (S) between the outer side-plates are shown; 

 while below X Y (at a lower level) are longitudinal canals (C). 



Fig.4. -Transverse Section of Specimen A, along X Y. 



from the Codonoblastids, in which they are somewhat broad and 

 petal-like; and from the Gi anatoblastids in which the ambulacra 

 stretch far down the ovoid theca. 



Hence we are led to place the blastoid in the Division Troosto- 

 BLASTiDiE — Family Troostocriniche, defined (vide Lankester, 

 Echinodermata) as Mastoids of elongate form with linear ambu- 

 lacra descending sharply outwards from the much restricted 

 peristome. 



This family (Troostocrinidfe) contains three main types, Troos- 

 tocrinus, Metablastus and Triccelocrinus. 



