Naviculacea.} iNFrsORiAT, animalcttles. 471 



from which it ditfera also by wanting the intciTnediatc rings between 

 the valves. 



PoDosiRA nummuhides = P. hormoides (Kiitz.) — Frustiilcs of a 

 depressed spheroidal form, united by their central pedicles, fidluni) 

 into a moniHform chain ; the stalks are colourless — the corpuscles 

 green and pimctate ; as many as seven have been seen united. Dia- 

 meter l-650th. On Polisiphonia, Callao, Peru. (P. 13, f. 45.) 



Y. Montaguei = Melosira glohifera (Ralfs.) — Corpuscles elliptic, 

 united by short stalks {isthmi.) Diameter 1 -600th. Antilles. 



Genus PoDOSPHENiA. — Simple, wedge-shaped (cuneiform) ; attached 

 when yoxmg by a pedicle, which, however, is sometimes obsolete ; they 

 often become free at a later period. The bivalve lorica is longer than 

 broad, with two openings at its broad anterior end ; granules yellowish 

 green, scattered mostly when young, but in older specimens united 

 into one or two, often stellate masses. Multiplication is by longitu- 

 dinal fission. Isolated segments (frustules) of Merdion and Echinella 

 are liable to be mistaken for those of Podosphenia ; but the first may 

 be distinguished by wanting, on their sm-face, the bands (vittae) indi- 

 cating internal septa. Kiitzing's description is " BaciUi on primary 

 side, cuneate ; on secondary side, obovate, lanceolate ; attached 

 stipes none (or obsolete.) " 



In the system of that naturalist, it is a member of the family 

 Licmophoreoe ; see genus of that name. 



P. gracilis. — Smooth, nan'owly wedge-shaped, rather acute at the 

 base ; (fig. 1 86 shewing a group attached to a thread-like filament, 

 whence they are often mistaken for Ecldnella: but in this case 

 the filament is not part of the creature, but merely the substance to 

 which it has adhered. It often covers Algse, Vorticella, Sertularia, &c. 

 At the lower part of the group, towards the right side, is represented 

 a side view of one laying across two others, shewn in front view ; in 

 the latter, delicate longitudinal striae are visible, and in the foimcr 

 the upper part of the lorica is rounded.) Length l-250th to 1-llOth. 

 North Sea and Baltic. 



P. abhreviata =P. Lynghyei. — Smooth, cuneate, broader and shorter 



than the preceding, base rather acute. Found upon Ceramium dia- 



phanum. (P. 16, t 13, b.) Length l-240th. North Sea and Baltic. 



'F. cuneafa = P. Ehrenbergii (Kixtz,) — Striated laterally on the 



