REPORT ON THE RADIOLARIA. 547 



central chamber. Patagium complete, spongy, with radiating beams, enveloping the whole disk, 

 with the exception of the outermost end of the arms, which is armed with twelve to sixteen strong 

 conical spines, the middle (perradial) spine much larger. 



Dimensions. — Eadius of each arm (without terminal spine) 0'18, l^asal breadth 0-025, terminal 

 breadth O'OS. 

 . Habitat. — South Atlantic, Station 333, surface. 



Genus 236. Tessarastrum,^ n. gen. 



Definition. — P o r o d i s c i d a with four simple, undivided, chambered arms, con- 

 nected by a patagium ; quadrangular shell bilateral, two opposite arms of the main axis 

 (or principal arms) different from the two others (or lateral arms). 



The genus Tessarastrum, formerly united by me with Histiastrum, differs from 

 the latter in its bilateral or symmetrical form, and bears therefore the same relation 

 to it that Ilagiastnim does to Stauralastrum. 



Subgenus 1. Tessarastrella, Haeckel. 

 Definition. — Both longitudinal arms of equal size and form. 



1. Tessarastrum straussii, n. sp. (PL 45, fig. 8). 



Histiastrum straussii, Haeckel, 1881, Prodromus et Atlas (pi. xlv. fig. 8). 



Cross not rectangular. Both principal arms of equal size and form, four times as long as 

 broad, and twice as long as the broader lateral arms ; the former with ten to eleven, the latter with 

 five to six joints, separated by convex transverse septa. Distal ends of the arms blunt. Axes of 

 the smaller arms not perpendicular to that of the larger arms ; therefore the anterior angles between 

 them smaller than the posterior angles. Patagium between the arms incomplete. I call this 

 remarkable species after the gi-eat German philosoiDher David Strauss. 



Dimensions. — EacUus of the principal arms 0'24, of the lateral arms 0'12 ; greatest breadth (in 

 the middle) of the former 0'05, of the latter 0'06. 



Habitat. — North Pacific, S'i/alone7na-ground, March 5, 1875. 



2. Tessarastrum spinozce, n. sp. 



Cross rectangular. Both principal arms of equal size and form, ten times as long as broad, and 

 twice as long as the lateral arms, whicli are only five times as long as broad. All arms linear, at 

 their distal end club-shaped, and armed with twenty to thirty very strong angular spines. Patagium 

 incomplete, enveloping only the basal half of the arms. (Picsembles Histiastrum boseanum, 



1 Tessarastrvm=Sta.TT\xlet with, four rays ; Tiaaet^et, aur^oi/. 



