APPENDIX. 427 



triangular siliceous lorica, triclentate, or corniculate, at 

 each lateral surface. They are multiplied under the ex- 

 ternal covering by longitudinal self-division. 



747. TRiCERATiuMfavus. Shell-like lorica triquetrous 

 laterally, plane or slightly convex, having the angles 

 obtuse ; the surface is marked with large hexagonal cells, 

 but on the back is a smooth central zone. Found fossil 

 in the chalk marl of Greece, and alive, in sea water, at 

 Cuxhaven. Diameter l-240th. 



748. TRICEBATIUM striolatum. Shell-like lorica trique- 

 trous laterally, convex, the angles being subacute ; surface 

 minutely punctated, back with a smooth central zone. 

 Found living, in sea water, at Cuxhaven. Size l-290th. 



Genus TBIPODISCUS belongs to the Bacillaria, section 

 Naviculaceae. Its members are free, and possess a round 

 bivalved siliceous lorica, having three appendiculated 

 processes, and dividing by longitudinal self-division. 



749. TBIPODISCUS Germanicus (Argus.") Lorica large, 

 orbicular, and compressed, with the valves slightly convex ; 

 the margin of the cells, which are disposed in radiating 

 series, being sometimes roughly punctated at intervals; 

 the lateral processes are short and hyaline. Colour green. 

 Found alive, in sea water, at Cuxhaven. Diameter l-220th. 



Genus ZYGOCEBOS belongs to the Bacillaria, section 

 Naviculaceae. Its members are characterized by being 

 free, and having a compressed, Navicula-shaped, bivalved 

 lorica, each end provided with two perforated horns. 

 Self-division longitudinal and complete. 



750. ZYGOCEBOS rhombus. Large, lorica turgid; viewed 

 laterally rhomboidal, and having rounded angles ; surface 

 marked with very delicate striae, the back having a 

 smooth central zone. Found alive, in sea water, at 

 Cuxhaven. In the l-96th of a line there are 24-26 striae. 

 Diameter 1 -290th. 



751. ZYGOCEBOS surirella. Small, lorica compressed; 



