Naviculacea.'\ ixfusokial animalcules. 449 



Tkicekatitjm Reticulum. — Smaller, granules small, uot radiating, 

 straight. Approaches T. Filcus. 



T. acutum. — Sides straight, apices acuminate, cells not radiant, 

 tcnin l-1150th. Diameter 1 -720th. Bermuda. 



T. condecorum. — Sides slightly convex, apices obtuse, surface 

 ornamented -v^-ith rows of fine granules in elegant curves, and 

 radiant ; granules fifteeu in 1-1 200th. Diameter 1-3 84th. Bermuda. 



T. Solemioceros. — Sides deeply concave, apices long, tubular, 

 radiant, subacute, sm-face covered -with gxanules, radiating in straight 

 lines; gi-anules fifteen in 1- 1200th. Diameter 1-2 76th. Bermuda. 



T. undulatum. — Sides rather convex and undulated ; undulations 

 three or four on each side ; surface adorned with minute granules, 

 disposed in elegantly curved radiating lines. Diameter 1 -480th. 

 Bermuda. 



T. Pileolus. — Veiy smaU, triangular, sides concave ; angles much 

 produced but obtuse ; surface with small scattered cells. Has the 

 form of T. Pileus, but the sculpturing and dimensions of T. Reticulum. 

 Diameter 1-5 76th. Southern Ocean. 



T. megastomum. — Triangular, sides straight ; central area hexangu- 

 lar, minutely but irregularly punctate ; apertures very large, entirely 

 occupying each of the angles. Diameter 1-1 200th. Fossil in African 

 and Peruvian Guano. 



T. Pileus. — Triangular, sides concave, angles produced, rather 

 acute, cells in radiating series ; smaller than those of T. favus. 

 Diameter 1 -288th. Fossil in Greek marl. 



T. comtum. (?) — Habit and general characters of T. favus, but has 

 each of its cells armed with a forked (fui'cate) spine. 



T. (dtcrnans (Bailey.) — Small, reticulated, ti'iangular ; surface 

 mai'ked with thi'ee lines, which, \\i\h. the portions cut off from the 

 sides, form a hexagonal figure. Common everj'where along the 

 Atlantic Coast, and in estuaries ; also abundant, in the fossil state, in 

 the infusorial strata of Virginia, and in the rice-fields of Georgia and 

 Carolina. 



Genus Zygocekos (Ehr.) — Free (?) compressed, navicula-shaped, 

 bivalve, siliceous ; each end provided with two perforated horns ; 

 self-division complete, hence frustiiles not concatenate. 



