AMONG SIMPLE SAECODE OE0ANISMS. 395 



Among the Thalamophora with thick, blunt, non-anastomosing 

 pseudopodia, must also be included a beautiful freshwater rhizo- 

 pod originally described by Wallich* under the name of Difflugia 

 symmetrica, and more recently studied by Fr. Eil. Schulze, who 

 has made it the type of an independent genus to which he assigns 

 the name of Quadrula (fig. 5)t. 



The test is pear-shaped, laterally compressed so as to be ellip- 

 tical in transverse section, and presents a definite sculpture 

 caused by its being composed of a great number of hyaline 

 square plates which touch one another by their edges. Qua- 

 drula is nearly allied to Hyalosphenia, from which it difiers mainly 

 in possessing a definitely sculptured test. The granular pro- 

 Fig. 5. 



Quadrula symmetrica. Viewed from the broad side. (After F. E. Schulze.) 



toplasm-body does not in general completely fill the test ; and 

 the space which intervenes between it and the test- walls is occu- 

 pied by a clear liquid and traversed by thin bands of protoplasm. 



In the centre of the more voluminous posterior or aboral portion 

 of the body lies the large clear spherical nucleus with a very distinct 

 dark nucleolus ; and in front of this are the pulsating vacuoles, 

 generally two in number. The pseudopodia are few, and are 



* Ann. Nat. Hist. vol. yiii. 1864. t Arch. f. mikr. Anat. vol. xi. 1875. 



