CHARACTERISTIC DEEP-SEA TYPES. 



RHIZOPODS. 



163 



Mexico, and Gulf Stream. The three (Fig. 493) or four armed 

 varieties often come up in great quantities in the dredge, and at- 

 tain a length of from 16 to 20 mm. R. ahyssoruin has a Avorld- 

 wide distribution ; it was discovered by the elder Sars, and de- 



Fig. 493. — Rliabdammina abyssorum. \. (Brady.) 



scribed in his first list of animals living in deep water off Norway. 

 This species presents many interesting modifications dependent 

 on external conditions, and its polymorphism seems remarkable ; 

 it is triradiate, quadriradiate, or a 

 straight tube, including all their possible 

 combinations. A small straiofht form 

 of the genus, R. linearis (Fig. 494), is 

 also frequent near the 500-fathom line. 



One of the species of Lituolinse, Reophax scorj/mrus, attains 

 a length of 10 mm. It builds its test loosely of siliceous sand 



Fig. 494. — Rhabdammina line- 

 f. (Brady.) 



aris. 



Fig. 49.5. 



Fig. 49.5 a. 



Reophax scorpiurus. 



8 



(Goes.) 



and sponge spicules. (Figs. 495, 495 a.) A widely spread form 

 crowded with nipple-shaped protuberances, Thuram/mina imjill- 



