N'aviculaeea.'] infttsortal animalcules. 491 



" The mode of growtli in this genus is very curious. In Biatoma. 

 as well as in most of the Budomem, the plant increases by a divisior. 

 of the frustules ; but, in this genus, as also in Biddulphia and Am- 

 phitetras, two new frustules arc formed within the old one, and as 

 they enlarge, rupture it, when it falls off. In these, the front por- 

 tion is at first very narrow, and merely a broad line, but it increases 

 greatly in breadth until the new fi'ustulcs are fiiUy formed." (Ealfs 

 Ann. Nat. Hist. 1843, p. 270.) 



The members of this genus are marine in habit, and seem to 

 prefer the colder northern seas — as the Northern Atlantic, but arc 

 absent in the Adriatic, and also in the Mediterranean. 



IsTHMiA oUiquata = I. nervosa, Kiitz. Nearly square, with small 

 marginal, hexagonal cells, disposed in parallel decussating lines, 

 with parallel ti-ansverse internal marginal septa; ventral portion 

 loosely cellular. Length of frustules l-90th. On marine Algae. 

 English Coast. 



" The frustules are usually not so wide in proportion to their 

 length, as in I. euervis.''' (Ralfs.) 



I. enervis. — Marginal cells tetragonal, larger, in transverse parallel 

 lines ; no internal septa. Form trepezoid, two to three times 

 broader than long. Length l-60th. Coasts of England and France. 

 On sea weed (P. 4, f. 183.) As opaque objects, they exhibit great 

 beauty under the microscope ; the different portions appearing like 

 reticulations, are shown in relief. 



I. (?) Africana (Ehr.) — Large flat fragments, resembling the 

 central portions of Isthmia, marked by transverse rows of very small 

 cells. Diameter of the largest fragment 1-2 16th. Oran, Africa. 



Genus Licmophoea (Kiitz.) — Bacilli (frustules) flabelliform ; in 

 front, narrowly cuneate ; on the other aspect linear, and rounded at 

 apex and base. Stipes thick, rigid. 



This genus gives name to the family Licmophorece of Kiitzing, 

 which includes, besides, the following genera : viz., Podosphenia, 

 Rhipidophora, and Climacosphenia. All the forms are marine. 



L. fulgens. — Frustules geminate, linear, rather wider near the 

 apex, truncate at each end, on the other side pe.'fectly linear ; stipes 

 short, tliick, dichotomous ; arrangement of fmstules on it radiating. 



K K 2 



