450 DESCiiiPTlON OF [Poli/gastnca. 



Zygoceeos Rhomhus. — Large ; testule laterally turgid and rhomboid, 

 angles rounded, surface with veiy fine granular stiiae ; dorsally with a 

 smooth central zone. Stria3 twenty-four to twenty-six in 1 -1150th. 

 Diameter 1 -290th. 



Z. Surirella. — Small, compressed laterally, lanceolate, with con- 

 stricted and obtuse apices ; surface with granular lines converging 

 to the centre; dorsally, with a wide smooth zone. Diameter 

 l-720th. Alive. (P. 14, f. 50, 51.) 



Z, {Denticella}) mohiliensis (Bailey.) — " Frustules quadrangular, 

 compressed, thin, delicately decussatedly-punctate ; lateral processes 

 slender; intennediate ones (two at each end) long and slender. 

 Colour yellowish. I first detected this species in 1848, in soimdings 

 from Mobile Bay, and subsequently at Savannah." 



Z. (?) Bipons. — Lanceolate laterally, each end acute ; and pro- 

 longed as a small horn, two shallow constrictions at the middle 

 surface delicately granular, not radiated. Diameter l-384th.Benniida. 



Z. (?) stiliger. — Surface loosely cellular, lorica produced into two 

 long acute styliform horns ; a double stricture about the middle, 

 laterally. Diameter 1-1 152nd. Bermuda. 



Of the two last species (says Ehi^enberg) I have seen but fragments, 

 and theii' true nature is therefore uncertain. Z. Stiliger may be a 

 species of Semiaulus ; but the constrictions in both resemble the 

 Biddul/phia, save that they are wanting of the wide apertures of the 

 horns. 



Z. (?) Australis. — Smooth, navicular, and turgid laterally ; horns 

 on the sides obsolete, apertures conspicuous. Diameter 1 -480th. 



Z. Navicula. — A species discovered in marl from ^gina. 



Sub-section II. Echinelle^. — Lorica simple, attached, with or 

 without a distinct stalk, (stipes.) 



Genus AcHNANTHES (Ehr.) TheStandard Shaped Animalcules. — Lorica 

 simple, composed of two or more pieces ; form prismatic, longer than 

 broad, with a central pore (umbilicus.) The individuals, solitary 

 or aggregate, are attached by a lateral pedicle (stipes) proceeding 

 from one end of their ventral surface. They are developed in the 

 form of simple pedicled chains (tablets or bands) resembling standards ; 

 self-division longitudinal with reference to individuals, but trans- 



