REPORT ON THE DIATOM ACE. K. 43 



Glyphodesrnis (Grev.), Cstr. 



It is by no means easy to define the two organisms which are represented on Plate 

 XVIII. figs. 12 and 13, in their valval and zonal aspects. Both are navicular, but the 

 one, which is elliptical iu form, is very much elongated, while the other has two lateral 

 protuberances. In the centre they possess a very pronounced nodule, as may be well 

 observed when they are viewed from their zonal sides. At each extremity the valve is 

 provided with a small but somewhat elevated cushion, which is extended and flat, and 

 acts as a support between two adjacent frustules of the series. The valve, which is 

 clathrate, is ornamented with quadrate granules disposed in parallel rows. 



Naviculoid clathrate valves provided with central nodules are to be found in the 

 Grevillean genus Gl yphodesmis, but in the latter there are no small terminal cushions 

 such as those present in the frustules represented in our present figures. In Plate x. 

 fig. 7, of the Quarterly Journal of Microscopical Science, vol. ii., new series, 1862, a series 

 of frustules of Gl yphodesmis eximia, Grev., is represented. These present in their zonal 

 aspects three projecting points which bring about a contact between adjoining frustules, 

 namely, a central one corresponding to the nodule, and two terminal ones. The last are 

 small smooth terminal cushions, and, although not distinctly marked, the presence of 

 terminal protuberances in all Glyphodesmides may be regarded as verified, and on 

 this account should be referred to in the definition of the s;euus. Hence the following 

 definition may be taken instead of that given by Greville : 1 — 



Frustulis seriatim conjunctis, valvis navicularibus, nodulo centrali et pulvinulis 

 terminalibus, structura clathrata, granulis transverse quadra to ordine dispositis, linea 

 centrali subconspicua. 



G-lyphodesmis murrayana, n. sp. (Plate XVIII. fig. 12.) 



Maxima, longe elliptica (novies lougior quani latior) ; structura clathrata, granulis 

 subquadratis quadrato ordine dispositis; pulvinulis terminalibus kevibus ellipticis ; area 

 centrali transverse elliptica, cui nodulum rotundum inscribitur. Ad insulas Philippinas. 



This frustule is remarkable on account of its size, elegance, and clearness of detail. 

 It is ornamented with large subquadrate granules which are arranged in parallel longi- 

 tudinal and transverse lines and give relief to the smooth oval extremities as well as to 

 the transversely elliptical central area where the large round nodule is conspicuous. When 

 viewed in the zonal aspect the central nodule is seen to be large, elevated, and somewhat 

 flattened at the top. It may also be noted that the nodule does not present an opening 

 or osteole so as to produce a communication between the surrounding medium and the 



1 Greville's definition ran as follows : " Frustules united into a filament ; lateral view naviculoid, with a 

 central nodule, median line, and transverse rows of granules ; structure clathrate, the granules being developed 

 within square cellules, arranged in parallel series." — Quart. Joum. Micr. Sci., vol. ii., new series, p. 234. 



