330 DESCRIPTION OF \ Poli/gasfrifa. 



CEE-iTAiJLTJS turgidus. — Poi-es aggi'egated in a band on the margin 

 of eacli valve of the testules. In foiin it is always tortuous. 

 Piameter 1 -432nd. Found in the Baltic Sea. 



Dr. Bailey describes this species as foUows : — "Frustules globular, 

 or slightly compressed, with two large rounded prominences at each 

 end, cohering by alternate angles, forming zigzag chains. Between 

 the two rounded processes, and in a plane at right angles to that 

 containing them, are placed two long horn-like processes. Two 

 frustules are often connected by an external decussately punctate 

 ceU, as in Isthnia and Biddidphia.''^ 



Genus Cebatoneis. — Indi^dduals solitary ; lorica prismatic, quad- 

 rangular, bivalve, and rostrate, with a central umbilicus, from which 

 two longitudinal fiuTows may be traced into the prolonged horns 

 (beaks.) Self-division complete ; hence indi^-iduals not chained, 

 though sometimes fomid in pairs. 



The general figui'e of Ccratoneis is that of Kavicida, but with the 

 apices much produced. In Klitziag's arrangement it is a member 

 of the family Wmiculete. 



C. Closterium. — Setaceous and lunate in figure ; central portions 

 linear lanceolate ; horns very long, twice the length of the body ; 

 granular contents brownish giiecn, occupying only the central part, 

 the horns being colourless ; lorica smooth ; in form it resembles 

 Closterium setaceiim ; movements active and gliding. Abundant in 

 the sea at Cuxhaven, &c. Length l-290th. to 1 -144th. Body 

 without horns, 1-1 150th. (P. 15, f. 59.) 



C. fasciola. — Linear lanceolate ; horns shorter than the body, but 

 curved in opposite directions, so that the lorica resembles the letter S. 

 The body without the horns is like Navicxila gracilis. Locomolion 

 distinct. Length l-430th. Cuxhaven. (P. 15, f. 60, 61.) 



C. Greta. — jSra\icular, smooth, rather constricted and flattened in 

 the middle; apices acute, straight, not much produced. (l-576th.) 

 Chalk marl, Sicily. 



C. laminaris. — Broadly lanceolate, transversely striated on the 

 margin ; beak short. Mexico. 



C. arcus. = JSfavimiJa arms. — Narrow, linear, curved, smooth ; 

 dorsxun convex, rather dilated in the centi'e of the ventral sui-face ; 



