448 DESCRIPTION OF [Polygastrica. 



long ; lateral surfaces with from 7 to 9 distinct transverse strise. 

 Found at Dolgelly, in Wales (P. 14, f. 24 and 25). 



" I was at first inclined to refer this plant to Ehrenberg's genus 

 TesseUo, but more minute examination convinced me that it could 

 not be placed there. The frustules are striated as in Striatella and 

 Tessella, but it difi'ers from the former genus in not being attached, 

 and from both, as the frustules do not cohere at the angles, forming 

 a chain. In the curious forms of the filament it difi'ers equally from 

 these genera and all the other Diatomaceae, except perhaps Tahella/ria, 

 in which the inflated canal produces a distinct resemblance. The 

 endochrome is of a dark green colour, and is often collected into an 

 irregular spot." 



Genus Tetea.gea.mma (Ehr.) — Lorica, bivalve, compressed, quad- 

 rate, free, unilocular, broader than long, with two pairs of septa 

 Avithin each cell interrupted (incomplete) in the middle, and there 

 expanded so as to produce the appearance of four musical notes. 

 This genus is allied to the peculiar Mexican genus Terpsinoe. Species 

 unknown. 



Genus Teiceeatium (Ehr.) — Individuals free, with a bivalve, tri- 

 angular lorica ; on each side tridentate or corniculate ; not concatenate ; 

 multiplied by longitudinal self-division. 



T. fanes. — Triquetral, plane or slightly convex on the sides, angles 

 obtuse, surface with hexangular cells, of large size and yellow in 

 colour, dorsum -with a smooth central zone. Diameter 1 -200th. 

 Alive at Cuxhaven, Vera Cruz, the Thames, &c., and fossil in chalk 

 marl of Greece and elsewhere. (P. 14, f. 43, 44.) 



T. striolatum. — Triquetral, with convex sides, and subacute angles ; 

 surface with very finely dotted lines ; dorsum with a smooth centi'al 

 zone. AUve. Diameter 1 -290th. 



T. oUustcm. — Large, triangular, with convex sides; angles widely 

 rounded, but less so than in T. amlhjoceros ; surface minutely dotted, 

 granules ten in 1-1 200th. 



T. (?) amblijoccros. — Large, triangular, with convex sides, and 

 widely rounded angles, ^dth very fine radiating rows of granules, of 

 which there are twenty-four in l-TiOOth. Diameter 1 -4.56th. 

 Virsinia. 



