78 



PROTOZOA 



B. ACANTHARIA. 



Order vii. Actinelida. — Radiul spines numerous, more than 20, 

 usually grouped irregularly. (Families 33-35.) Xiphacantha Haeck. 



Order viii. Acanthonida. — Radial spines equal. (Families 36-38.) 



Order ix. Sphaerophracta. • — Radial spines 20, with a latticed 

 spherical shell, independent of, or formed from the reticulations of 

 the spines. (Families 39-41.) Dorataspis Haeck. (Fig. 25, A). 



Order x. Prunophracta. — Radial spines 20, unequal ; latticed shell, 

 ellipsoidal, lenticular, or doubly conical. (Families 42-44.) 



Fio. 2i.—X iphacaiUha (Acantluiria). From tlie surface. The skeleton only, x IflO. 

 (From Wyville Thomson.) 



Nassellakia. 



Order xi. Nassoidea. — Skeleton absent. (Family 45.) 



Order xii. Plectoidea. — Skeleton of a single l)ranching spicule, the 



l:)ranches sometimes reticulate, l)ut never forming a latticed shell or 



a sagittal ring. (Families 46-47.) 

 Order xiii. Stephoidea. — Skeleton with a sagittal ring continuous 



with the branched spicule, and sometimes other rings or branches. 



(Families 48-51.) Lithocercus Theel (Fig. 26, A). 

 Order xiv. Spyroidea. — Skeleton with a latticed shell developed 



around the sagittal ring (cephalis), and constricted in the sagittal plane,. 



with a lower chamber (thorax) sometimes added. (Families 52-55.) 



