APPENDIX. 427 



triangular siliceous lorica, tridentate, or corniculate, at 

 each lateral surface. They are multiplied luider the ex- 

 ternal covering by longitudinal self-division. 



747. TRiCERATivrnJavHs. — 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. Triceratium slriolatum. — 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 1-2 90th. 



Genus Tripodiscus 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. Tripodiscus Gennanicus (Argus.) — Lorica large, 

 orbicular, and compressed, wdth 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 Zygoceros 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. Zygoceros rhombus. — Large, lorica turgid; vicAved 

 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. Zygoceros surirella. — Small, lorica compressed; 



