234 GREVILLE, ON NEW DIATOMS. 



out tlie space and was in the process of becoming obsolete, 

 which is not improbable. There is, however, no trace of the 

 remains of cellulation attached to the rest of the boundary of 

 the blank space. The remarkable spine-like process which 

 occurs in T. marginatum and pulcherrimum at the apices of 

 the central triangle is very conspicuous in the present diatom. 

 I have great pleasure in dedicating this rare species to 

 Dr. Davy, who collected and brought home the material in 

 which it Avas discovered. 



COCCONEIS. 



Cocconeis ccelata, n. sp., Walk.-Arn., MS. — Valve oval or 

 oblong, with two longitudinal lines (one on each side the 

 median line), constricted opposite the nodule, and forcipate 

 towards the apices ; transverse costse distant, flat, and con- 

 tinuous in substance with the median and longitudinal lines. 

 Length -0005" to -0018". (Figs. 5, 6.) 



Hab. New Zealand, on Ballia ; Professor Walker- Arnott. 



A most singular and beautiful species. The markings are 

 arranged upon the plan of Navicula forcipata and its allies. 

 There is a median line and two longitudinal ones ; the latter 

 constricted opposite the nodule, and connected together by 

 means of the nodule, which is expanded into a broad, stauros- 

 like bar. They then curve outwards and become forcipate 

 towards the ends. The transverse lines or eostae are remote 

 (about 10 in 'OOl"), somewhat concentric, with extremities. 

 All the lines are flat or compressed and continuous in 

 substance with each other, the whole having a curious 

 skeleton-like appearance, as if an epidermis had been re- 

 moved. 



Glyphodesmis, n. gen., Grev. 



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. 



At first sight the filament of this diatom might almost 

 pass for that of an Odontidium. It also resembles a Plagio- 

 gramma, wanting only the pervious costse. Indeed, the 

 likeness between it and P. ornatum ('Mic. Journ.,^ vol. vii, 

 PI. X, fig. 9) is, with that exception, very striking. But 

 the side view of the frustule exhibits a totally diflerent 

 structure. There is a large, prominent, central nodule, a 

 decided median line, and thick, transverse moniliform striae, 

 which, when closely examined; are found to be composed of 



