434 APPENDIX. 



Greece, and alive at Kiel and Cuxhaven. In the living 

 forms the cells were filled with a soft greenish matter, 

 in which vesicles and very minute granules were seen. 

 Locomotion was perceptible after long observation. 

 Diameter 1 -860th. 



218. GALLIONELLA sulcata. Found fossil in the 

 chalk marl of Caltanisetta, Oran, Zante, and Greece ; and 

 living, in sea water, at Cuxhaven. 



779. HALLIOMMA (?) radians. External joints not 

 separating, shape globose, sub-ovate ; the siliceous lorica 

 having holes in it, and on all sides cells radiating from the 

 obscure central nucleus. Found fossil in the chalk marl of 

 Greece, and alive in sea water at Cuxhaven. Locomotion 

 not observable ; creature crystalline. Diameter l-56Uth. 



780. NAVICULA didymus. Shell-like lorica striated; 

 viewed from the side linear, truncated at both ends, and 

 whole ; viewed dorsally, constricted in the middle ; both 

 ends sub-orbicular, thus appearing as if formed of two discs 

 joined together. In 1-1 00th of a line there are twenty- 

 three striae. Found fossil in the chalk marl of Caltanisetta, 

 and living, in sea water, at Cuxhaven, Wismar, &c. This 

 species was first observed in the live condition, afterwards 

 fossil, in Sicily. Similar forms are very numerous in the 

 chalk marl of Greece. It is distinguished from the 

 two following (N. entomon and N. gemma) by the want 

 of the constriction when viewed on the lateral surface ; 

 on the ventral surface two green ova plates are seen, 

 divided by a broad central colourless stripe. Length 

 1-1 150th to l-480th. 



781. NAVICULA entomon. Shell-like lorica striated when 

 viewed from either surface, constricted in the centre, striae 

 very broad. Found fossil in the chalk marl of Greece, 

 and alive, in sea water, at Christiana. In the 1- 100th of a 

 line are eighteen striae; the two halves of this species ap- 

 pear more of a long figure than a round one. Length of 

 the fossil forms l-432nd; of the living, l-290th. 



