Naviculacea.] infusorial animalcules. 433 



In the absence of the ring (by which is meant the intermediate 

 circular band), Py.r«V/(V«/tf differs from Goniothecium. (See that genus.) 

 Pyxidiciila differs from Coscinodiscus by having its patelhc (valves) 

 always contiguous, not conjoined by an intervening annular band. 

 Pyxidicuh also differs from J)iscoj)Iea, in the recent state, by its convex 

 non-involuted patella?. In the fossil state this character vanishes, 

 hence there will always arise a difficulty respecting fossil forms. 



The genus ryxidlcula, has been sub-divided into several genera 

 and sub-genera, by Ehrenberg ; Wz., the genera Mastogonia, Stephano- 

 gonia, and the sub-genera Lidyopyxis, Stephanopyxis, and Xanthio- 

 pyxis ; moreover, the newly constituted genera Goniothecium and 

 Rhizoselenia are closely allied to it. 



P. operciilata. — Transparent and spherical , containing yellowish- 

 green granular matter (group 127, the upper figure is a group at 

 right angles to that di'aAvn on the left, shewing the furrow by which 

 it separates ; the figure to the right is a detached half; in the lower 

 fig-ure a transparent globular (glandular, Ehr.) body is observed.) No 

 locomotion has been seen. Eound abundantly in Autumn, in fresh- 

 water ponds, along with Naviculece. Hampstead Ponds. Diameter 

 1- 1440th. to l-oVOth. 



P. glohator. — I insert under this name the globular bodies referred 

 to above, found in flints. The section of pebble, containing the 

 specimen from which Mr. Bauer's di'a wing in p. 12, figs 506 and 510 

 were made, was found on Brighton Beach. The figures ai'e mag- 

 nified 100 diameters. 



P. a2)p>endicidata. — Subglobose ; surface with cells in rows ; a 

 short eccentric cornu (appendix) proceeds from each segment 

 (patella.) Diameter 1-G24th. Eichmond, Virginia. 



P. areolata. — Surface of the centre of patelhe, punctate-arcolate ; 

 areolae heptagonal, with seven lateral, dotted areola). Diameter 

 1 - 9 6 th . Petersburg, Virginia . 



P. apiculata. — Oblong, sub-cylindrical, widely roimded on each 

 side ; stu'face of patellae cellular, cells in longitudinal rows ; each 

 extremity hispid at the centre, with projecting points (apiculi). 

 Diameter 1- 888th. Virginia and ^gina. 



p. Coscinodiscus. — Testules Avith a pair of cUscoid patella) ; surface 



