422 DKSCHiPTiON OF [Polygastrica, 



14, 1850, p. 308), has described this species as a Navictila, but 

 the transverse striae determine it to be a Pinnularia in Ehren- 

 berg's plan. 



Sub-genus Biploneis. — The three following species have been 

 described by Ehrenberg under the name of Biphneiz, by which 

 appellation it would seem he wishes to designate a sub-section of 

 Pinmdaria, having some distinguishing peculiarity, which, however, 

 has not been met with in his writings. 



From the figiu'e of Bifloneis Didyma, it may be presumed that 

 Ehrenberg intends this sub-genus to include Pimiularia, constricted 

 at the middle, in the dorsal and ventral aspect, and having, so to 

 speak, a double {diplos Gr.) outline. 



D. JBombus. — Constricted, with sub-cordate segments ; apices sub- 

 acute ; strise dense, granular, twenty-one in l-12001h. ; granules 

 of the largest striae in fours. Length 1 -384th. FossO in the 

 chalk marl of ^gina. 



D. crabro. — Constricted, with widely separated elongate lanceolate 

 lobes, subacute or obtuse ; striae strong but smooth ; eleven to twelve 

 in l-1200th. Length l-276th. In chalk marl from JEgina. 



D. Didtjma. = Pinnularia Didyma. (P. 24, f. 12.) 



Sub-genus Statjeoneis (Ehr.) — Lorica smooth, or longitudinally 

 striped ; median aperture (umbilicus) transverse ; but no transverse 



striae. 



Under this name Kiitzing includes all Navicxdce with a transverse 

 median aperture, whether striated transversely or not. 



S. Plioenicenteron f Cymlella, Agardh.)— Smooth, of an elongated 

 lanceolate fonn, with rather obtuse tapering ends ; longitudinal 

 striae rare. It is very motile. Ponds, Hampstead ; and fossil at San 

 Fiore, in Tuscany. Length l-400th. to l-140th. (P. 3, f. 139, and 

 p. 15, f. 17 and 18.) 



S. platystoma. — Smooth, linear lanceolate, apices produced, widely 

 truncate ; central opening transverse, (fig. 142.) Length 1-1 100th. 

 to l-240th. 



S. ampMlepta. — Narrowly lanceolate, ends constricted, sub-capitate, 

 rounded. Chili. 



S. aneeps. — Smaller than preceding; naiTow, linear lanccolato 

 ends constricted, sub-capitate, and truncate. Cayenne. 



