334 



GLYPHODESMIS. 



Tribe x. Plagiogramme^e. 



Valves showing in the median portion a transverse hyaline space. . Plagiogramma. 



f Valves without a central pseudo-nodule . . Dimeregramma. 



Pseudo-nodule very coarse, projecting ; 



Valves without 



a transverse 

 hyaline space. 



I 



Valves 

 furnished 

 with a 

 central 

 nodule. 



valves cuneate 



Omphalopsis. 



| Central nodule rather small ; valves 



(_ not cuneate 



. Glyphodesmis. 



GENUS 55. GLYPHODESMIS GREV, 1862. 



Valves navicular, furnished with a central 

 pseudo-nodule and terminal smooth spaces. 

 Pseudo-raphe distinct. Puncta more or less 

 quadrangular, usually arranged in longitudinal 

 and transverse rows. Girdle face quadrangu- 

 lar, attenuate between the smooth apices and 

 the connecting .zone. Frustules united in 

 filaments. 



Authors have enumerated a dozen forms of 

 Glyphodcsmis, but many of these do not really 

 belong to the genus. The two following, coming 

 from the North Sea, are true types of the genus. 



Fig. 91. 



Glyphodestnis Wilhamsonii. 



a. Girdle view. b. Valve view 



ANALYSIS OF SPECIES. 



Beads rather small, extending throughout the valve, frustule attenuate 

 between the central nodule and the smooth spaces . . . G. Williamsonii. 



Beads very coarse, marginal ; frustules somewhat attenuate between the 

 smooth apices . . . . . . G. distans. 



Glyphodesmis Williamsonii (Greg.) Grun. (H.v.H. 



At)., pi. 36, f. 14*; Diadesmis Willia?nsonii Greg.! Diat. of Clyde, p. 25, 

 pi. 2, f. 40*), plate 30, fig. 847. 



Valve linear, narrow, constricted at the median portion, with apices produced- 

 rostrate. Pseudo-raphe very conspicuous, dilated round the central pseudo- 

 nodule and at the apices, where it leaves an oblong smooth space. Striae 

 formed of coarse sub-quadrangular granules, forming longitudinal and trans- 

 verse rows, the latter about 8 in 1 c.d.m. Girdle face quadrangular, attenuate 

 between the central nodule and the smooth spaces ; similarly attenuate (on 

 the short margin of the frustule) between the smooth spaces and the connect- 

 ing zone. Length, 6 to 8 c.d.m. 



Marine. Coasts of England (Kitton), Scotland (Loch Fyne, Greg. !) and of Ireland. 



