Naviculacea.'] infusorial animalcules. 463 



species, very evident, in others scarcely discernible, and so assist in 

 forming specific characters. There are also two obscui'e pimcta at 

 the base, and generally a single slight notch neai- the middle of each 

 lateral margin. The lateral siu'faces are generally transversely 

 striated, and have a longitudinal pellucid line running down the 

 centre." 



The species of Gomphonema are especially of fresh-water habit, 

 growing on filiform Algae ; but some few are found in the sea ; many 

 too, occiir in a fossil state, but then only as isolated, detached 

 fi:ustules. 



Propagation by conjugation has been witnessed in this family, viz., 

 in G. dlchotomum, G. minutissimum, and G. constrictum. (See P. 14 

 f. 9 to 12, and 17 also.) 



Goifi'HoxEJiA truncatum ( Vorticella pyraria, M.) — Striated. Group 

 187, and P. 4, figs. 188 to 190, represent various views, both separate, 

 and attached ; these will convey a far better idea of their form, and 

 the mode of attachment of the genus, than any verbal description. 

 Separated frustules move distinctly. Found free in water and upon 

 Lemna, &.c. and fossil, at Franzenbad and San Fiore. Length 1-1 720th 

 to 1 -280th. 



G. capitatum. — Striated, elongated, cuneiform, constricted near 

 the wider extremity, forming a short neck, surmounted by a 

 widely-rounded, truncate head. Stipes long, dichotomous, jointed. 

 Length l-1720th to l-280th. Occurs both alive and fossil 

 throughout Eiu'ope. 



G. Gracile = G. dichotomum (Kiitz. and Ealfs.) — Elongated, 

 cuneate ; terminal puncta very minute ; lateral surfaces lanceolate, 

 faintly striated ; stipes slender, much branched dichotomously. The 

 frustules somewhat resemble those of G. oUvacea, but are larger and 

 narrower, and their puncta far less distinct (Ralfs.) Length 

 1-1 150th to l-860th. 



This and the preceding species form a brownish-yellow slime upon 

 water plants, especially in spring. 



G. acuminatum = G. minutum (Agardh and Ralfs.) — Frustules 

 elongated, wedge-shaped, striated, -s^dth a dilated and pointed head 

 or crest, surmoimting a constriction; laterally veutricose at the middle. 

 Length 1- 860th; sometimes from 1- 720th to l-430th. Found fossil, 



